delb

delb is a library that provides an ergonomic model for XML encoded text documents (e.g. TEI-XML) for the Python programming language. It fills a gap for the humanities-related field of software development towards the excellent (scientific) communities in the Python ecosystem.

For a more elaborated discussion see the Design chapter of the documentation.

Features

• Loads documents from various source types. This is customizable and extensible.

• XML DOM types are represented by distinct classes.

• A completely type-annotated API.

• Consistent design regarding names and callables’ signatures.

• Shadows comments and processing instructions by default.

• Querying with XPath and CSS expressions.

Development status

You’re invited to submit tests that reflect desired use cases or are merely of theoretical nature. Of course, any kind of proposals for or implementations of improvements are welcome as well.

Related Projects & Testimonials

snakesist is an eXist-db client that uses delb to expose database resources.

Kurt Raschke noted in 2010:

In a DOM-based implementation, it would be relatively easy […]
But lxml doesn't use text nodes; instead it uses [text] and [tail]
properties to hold text content.

About the design

tl;dr

lxml resp. libxml2 are powerful tools, but have an unergonomic data model to work with encoded text. Let’s build a DOM API inspired wrapper around it.

Aspects & Caveats

The library is partly opinionated to encourage good practices and to be more pythonic. Therefore its behaviour deviates from lxml and ignores stuff:

• Serializations of documents are UTF-8 encoded by default and always start with an XML declaration.

• Comment and processing instruction nodes are shadowed by default, see delb.altered_default_filters() on how to make them accessible.

• CDATA nodes are not accessible at all, but are retained and appear in serializations; unless you [DANGER ZONE] manipulate the tree. Depending on your actions you might encounter no alterations or a complete loss of these nodes within the root node. [/DANGER ZONE]

If you need to apply bad practices anyway, you can fall back to tinker with the lxml objects that are bound to TagNode._etree_obj.

Reasoning

XML can be used to encode text documents, examples for such uses would be the Open Document Format and XML-TEI. It’s more prevalent use however is to encode data that is to be consumed by algorithms as configuration, measurements, application events, various metadata and so on.

Python is a high-level, general programming language with a vast ecosystem, notably including diverse scientific communities and tools. As such it is well suited to solve and cause problems in the humanities related field of Research Software Engineering by programmers with diverse educational background and expertise.

The commonly used Python library to parse and interact with a representation of an XML document is lxml. Other libraries like the xml.etree.ElementTree module from the Python standard library shall not be discussed due to their insignificance and shortcomings. It is notable that at least these two share significant design aspects of Java APIs which is perceived as weird and clumsy in Python code. lxml is a wrapper around libxml2 which was developed by the GNOME developers for other data than text documents. Data that is strictly structured and expectable. Text documents are different in these regards as natural languages and variety of media allow and lead to unprecedented manifestations for which an encoding mixes different abstracted encapsulations of text fragments. And they are formulated and structured for human consumers, and often printing devices.

So, what’s wrong with lxml? Not much, it’s a rock-solid, fast API for XML documents with known issues and known workarounds that represents the full glory of what a full-fledged family of specification implies - of which a lot is not of concern for the problems at hand and occasionally make solutions complicated. The one aspect that’s very wrong in the context of text processing is unfortunately its central model of elements and data/text that is attached to it in two different relations. In particular the notion of an element tail makes the whole enchilada tricky to traverse / navigate. The existence of this attribute is due to the insignificance of these fragments of an XML stream in the aforementioned, common uses of XML.

Now it is time for an example, given this document snippet:

<p rendition="#justify">
  <lb/>Nomadisme épique exploratori-
  <lb/><space dim="horizontal" quantity="2" units="chars"/>sme urbain <hi rendition="#b">Art des voya-
  <lb/><space dim="horizontal" quantity="2" units="chars"/>ges</hi> et des promenades
</p>

Here’s a graphical representation of the markup with etree’s elements and their text and tail attributes:

When thinking about a paragraph of text, a way to conceptualize it is as a sequence of sentences, formed by a series of words, a sequence of graphemes, and punctuation. That’s a quite simple cascade of categories which can be very well anticipated when processing text. With that mental model, line beginnings would rather be considered to be on the same level as signs, but “Nomadisme …” turns out not to be a sibling object of the object that represents the line beginning and is not in direct relation with the paragraph. In lxml’s model it is rather an attribute tail assigned to that line beginning. The text contents of the object that represents the hi element and its children give a good impression how hairy simple tasks can become.

An algorithm that shall remove line beginnings, space representations and concatenate broken words would need a function that removes the element objects in question while preserving the text fragments in its meaningful sequence attached to the text and tail properties. In case these have no content, their value of None leads to different operations to concatenate strings. Here’s a working implementation from the inxs library 1 for that data model:

def remove_elements(
    *elements: etree.ElementBase,
    keep_children=False,
    preserve_text=False,
    preserve_tail=False
 ) -> None:
    """ Removes the given elements from its tree. Unless ``keep_children`` is
        passed as ``True``, its children vanish with it into void. If
        ``preserve_text`` is ``True``, the text and tail of a deleted element
        will be preserved either in its left sibling's tail or its parent's
        text. """
    for element in elements:
        if preserve_text and element.text:
            previous = element.getprevious()
            if previous is None:

                parent = element.getparent()
                if parent.text is None:
                    parent.text = ''
                parent.text += element.text
            else:
                if previous.tail is None:
                    previous.tail = element.text
                else:
                    previous.tail += element.text

        if preserve_tail and element.tail:
            if keep_children and len(element):
                if element[-1].tail:
                    element[-1].tail += element.tail
                else:
                    element[-1].tail = element.tail
            else:
                previous = element.getprevious()
                if previous is None:
                    parent = element.getparent()
                    if parent.text is None:
                        parent.text = ''
                    parent.text += element.tail
                else:
                    if len(element):
                        if element[-1].tail is None:
                            element[-1].tail = element.tail
                        else:
                            element[-1].tail += element.tail
                    else:
                        if previous.tail is None:
                            previous.tail = ''
                        previous.tail += element.tail

        if keep_children:
            for child in element:
                element.addprevious(child)
        element.getparent().remove(element)

That by itself is enough to simply remove the space elements, but also considering word-breaking dashes to wrap everything up is a similar piece of routine of its own. And these quirks come back to you steadily while actual markup is regularly more complex.

Now obviously, the data model that lxml / libxml2 provides is not up to standard Python ergonomics to solve text encoding problems.

There must be a better way.

There is a notable other markup parser that wraps around lxml, BeautifulSoup4. It carries some interesting ideas, but is overall too opinionated and partly ambiguous to implement a stringent data model. A notable specification of a solid model for text documents is the DOM API that is even implemented in the standard library’s xml.dom.minidom module. But it lacks an XPath interface and rumours say it’s slow. To illustrate the more accessible model with a better locatability, here’s another graphical representation of the markup example from above with text content in an emancipated, dedicated node type:

Note that text containing attributes appear in document order which promises an eased lookaround. So, the obvious (?) idea is to wrap lxml in a layer that takes the DOM API as paradigmatic inspiration, looks and behaves pythonic while keeping the wrapped powers accessible.

Now with that API available, this is what an equivalent of the horribly complicated function seen above would look like:

@altered_default_filters()
def remove_nodes(*nodes: NodeBase, keep_children=False):
    """ Removes the given nodes from its tree. Unless ``keep_children`` is
         passed as ``True``, its children vanish with it into void. """
    for node in nodes:
        node.detach(retain_child_nodes=keep_children)

Frequently Asked Questions

Isn’t XML an obsolete format for text encoding, invented by boomers and cynically held up by their Generation X apologists? Why don’t you put your efforts in developing new approaches such as storing text in a graph database?

We think that XML-based encodings are actually very well suited for long-term usable text representations with a broad potential for granularity of capturing and semantic annotations. Not only is the data format simple enough to hold a full artifact in a self-contained file, but we also consider the duality of a format that can be handled both as stream and as tree as a helpful feature to address the physical and logical dimensions of a text and its manifestation. That is advantageous over depending on a heavy-weight database system. We acknowledge unquestionably that the specifications in the XML universe are often over-engineered, partly stuck in the times of their genesis and thus (euphemistically put) no fun. As a direct result of that the availability of implementations for contemporary development contexts and their ergonomics are poor, if available at all for a platform. That is what delb is addressing.

What are your long-term goals with this project?

Currently we want to flesh out a concluded user interface that lets developers concentrate on their tasks and not on the shortcomings and idiosyncrasies of available tools in the Pythoniverse. After modeling that API as a wrapper around lxml the aim is now to replace it piece by piece with a Pure Python™ implementation that will later be transpiled to C extension code with mypyc.

Eventually we’d like to re-conquer the world wide web and make unagitated, long texts and Stooges clips its predominant content again. On that occasion, fuck you Mark, fuck off Jeff, go fuck yourself Peter and all the other fucknut character masks. What a disgusting misery it is that the capital created from Tim’s ideas.

1

The inxs library failed. Yet it made clear which layer in Python XML Text handling needs to be fixed.

Installation

From the Python Package Index

To install delb manually, not as dependency, use pip:

$ pip install delb

At the moment there’s only one optional dependency to enable document loading via http and https, to include it use:

$ pip install delb[https-loader]

From source

Prerequisites:

• A virtual environment of your project is activated.

• That virtual environment houses an interpreter for Python 3.7 or later.

Obtain the code with roughly one of:

• git clone git@github.com:delb-xml/delb-py.git

• curl -LosS https://github.com/delb-xml/delb-py/archive/main.tar.gz | tar xzf -

To install it regularly:

…/delb-py $ pip install .

Again, to include the loading over http(s):

…/delb-py $ pip install .[https-loader]

For developing purposes of delb itself, the library should be installed in editable mode:

…/delb-py $ pip install --editable .

Hint

Using git submodules is a great way to vendorize a lib for your project and to have a fork for your adjustments. Please offer the latter to upstream if done well.

Developer toolbox

The repository includes configurations so that beside a suited Python interpreter three tools need to be available globally. pipx is the recommended facilitation to install the Python implemented tools black and hatch.

just

just is a task runner that executes a variety of common recipes. This gives a list of all available ones:

…/delb-py $ just --list

Before committing changes, run the complete suite of quality checks by invoking the default recipe:

…/delb-py $ just

black

It’s recommended to configure the used editors and IDEs to enforce black’s code style, but it can also be applied with:

…/delb-py $ just black

hatch

Several of the just recipes rely on hatch.

API Documentation

Note

There are actually two packages that are installed with delb: delb and _delb. As the underscore indicates, the latter is exposing private parts of the API while the first is re-exposing what is deemed to be public from that one and additional contents. As a rule of thumb, use the public API in applications and the private API in delb extensions. By doing so, you can avoid circular dependencies if your extension (or other code that it depends on) uses contents from the _delb package.

Documents

class delb.Document(source, collapse_whitespace=None, parser=None, parser_options=None, klass=None, **config)

This class is the entrypoint to obtain a representation of an XML encoded text document. For instantiation any object can be passed. A suitable loader must be available for the given source. See Document loaders for the default loaders that come with this package. Plugins are capable to alter the available loaders, see Extending delb.

Nodes can be tested for membership in a document:

>>> document = Document("<root>text</root>")
>>> text_node = document.root[0]
>>> text_node in document
True
>>> text_node.clone() in document
False

The string coercion of a document yields an XML encoded stream, but unlike Document.save() and Document.write(), without an XML declaration:

>>> document = Document("<root/>")
>>> str(document)
'<root/>'

Parameters

• source – Anything that the configured loaders can make sense of to return a parsed document tree.

• collapse_whitespace – Deprecated. Use the argument with the same name on the parser_options object.

• parser – Deprecated.

• parser_options – A delb.ParserOptions class to configure the used parser.

• klass – Explicitly define the initilized class. This can be useful for applications that have default document subclasses in use.

• config – Additional keyword arguments for the configuration of extension classes.

Properties

config	Beside the used parser and collapsed_whitespace option, this property contains the namespaced data that extension classes and loaders may have stored.
head_nodes	A list-like accessor to the nodes that precede the document's root node.
namespaces	The namespace mapping of the document's root node.
root	The root node of a document tree.
source_url	The source URL where a loader obtained the document's contents or None.
tail_nodes	A list-like accessor to the nodes that follow the document's root node.

Uncategorized methods

cleanup_namespaces([namespaces, retain_prefixes])	Consolidates the namespace declarations in the document by removing unused and redundant ones.
clone()	return Another instance with the duplicated contents.
collapse_whitespace()	Collapses whitespace as described here: https://wiki.tei-c.org/index.php/XML_Whitespace#Recommendations
css_select(expression[, namespaces])	This method proxies to the TagNode.css_select() method of the document's root node.
merge_text_nodes()	This method proxies to the TagNode.merge_text_nodes() method of the document's root node.
new_tag_node(local_name[, attributes, namespace])	This method proxies to the TagNode.new_tag_node() method of the document's root node.
save(path[, pretty])	param path The path where the document shall be saved.
write(buffer[, pretty])	param buffer A file-like object that the document is written to.
xpath(expression[, namespaces])	This method proxies to the TagNode.xpath() method of the document's root node.
xslt(transformation)	param transformation A lxml.etree.XSLT instance that shall be

---

cleanup_namespaces(namespaces: Optional[Mapping[Optional[str], str]] = None, retain_prefixes: Optional[Iterable[str]] = None)

Consolidates the namespace declarations in the document by removing unused and redundant ones.

There are currently some caveats due to lxml/libxml2’s implementations:

• prefixes cannot be set for the default namespace

• a namespace cannot be declared as default after a node’s creation (where a namespace was specified that had been registered for a prefix with register_namespace())

• there’s no way to unregister a prefix for a namespace

• if there are other namespaces used as default namespaces (where a namespace was specified that had not been registered for a prefix) in the descendants of the root, their declarations are lost when this method is used

To ensure clean serializations, one should:

• register prefixes for all namespaces except the default one at the start of an application

• use only one default namespace within a document

Parameters

• namespaces – An optional mapping of prefixes (keys) to namespaces (values) that will be declared at the root element.

• retain_prefixes – An optional iterable that contains prefixes whose declarations shall be kept despite not being used.

clone() → Document

Returns

Another instance with the duplicated contents.

collapse_whitespace()

Collapses whitespace as described here: https://wiki.tei-c.org/index.php/XML_Whitespace#Recommendations

Implicitly merges all neighbouring text nodes.

config: SimpleNamespace

Beside the used parser and collapsed_whitespace option, this property contains the namespaced data that extension classes and loaders may have stored.

css_select(expression: str, namespaces: Optional[Namespaces] = None) → QueryResults

This method proxies to the TagNode.css_select() method of the document’s root node.

head_nodes

A list-like accessor to the nodes that precede the document’s root node. Note that nodes can’t be removed or replaced.

merge_text_nodes()

This method proxies to the TagNode.merge_text_nodes() method of the document’s root node.

property namespaces: Namespaces

The namespace mapping of the document’s root node.

new_tag_node(local_name: str, attributes: Optional[Dict[str, str]] = None, namespace: Optional[str] = None) → TagNode

This method proxies to the TagNode.new_tag_node() method of the document’s root node.

property root: TagNode

The root node of a document tree.

save(path: Path, pretty: bool = False, **cleanup_namespaces_args)

Parameters

• path – The path where the document shall be saved.

• pretty – Adds indentation for human consumers when True.

• cleanup_namespaces_args – Arguments that are a passed to Document.cleanup_namespaces() before saving.

source_url: Optional[str]

The source URL where a loader obtained the document’s contents or None.

tail_nodes

A list-like accessor to the nodes that follow the document’s root node. Note that nodes can’t be removed or replaced.

write(buffer: IO, pretty: bool = False, **cleanup_namespaces_args)

Parameters

• buffer – A file-like object that the document is written to.

• pretty – Adds indentation for human consumers when True.

• cleanup_namespaces_args – Arguments that are a passed to Document.cleanup_namespaces() before writing.

xpath(expression: str, namespaces: Optional[Namespaces] = None) → QueryResults

This method proxies to the TagNode.xpath() method of the document’s root node.

xslt(transformation: XSLT) → Document

Parameters

transformation – A lxml.etree.XSLT instance that shall be applied to the document.

Returns

A new instance with the transformation’s result.

Document loaders

If you want or need to manipulate the availability of or order in which loaders are attempted, you can change the delb.plugins.plugin_manager.plugins.loaders object which is a list. Its state is reflected in your whole application. Please refer to this issue when you require finer controls over these aspects.

Core

The core_loaders module provides a set loaders to retrieve documents from various data sources.

_delb.plugins.core_loaders.buffer_loader(data: Any, config: SimpleNamespace) → _delb.typing.LoaderResult

This loader loads a document from a file-like object.

_delb.plugins.core_loaders.etree_loader(data: Any, config: SimpleNamespace) → _delb.typing.LoaderResult

This loader processes lxml.etree._Element and lxml.etree._ElementTree instances.

_delb.plugins.core_loaders.ftp_loader(data: Any, config: SimpleNamespace) → _delb.typing.LoaderResult

Loads a document from a URL with either the ftp schema. The URL will be bound to source_url on the document’s Document.config attribute.

_delb.plugins.core_loaders.path_loader(data: Any, config: SimpleNamespace) → _delb.typing.LoaderResult

This loader loads from a file that is pointed at with a pathlib.Path instance. That instance will be bound to source_path on the document’s Document.config attribute.

_delb.plugins.core_loaders.tag_node_loader(data: Any, config: SimpleNamespace) → _delb.typing.LoaderResult

This loader loads, or rather clones, a delb.TagNode instance and its descendant nodes.

_delb.plugins.core_loaders.text_loader(data: Any, config: SimpleNamespace) → _delb.typing.LoaderResult

Parses a string containing a full document.

Extra

If delb is installed with https-loader as extra, the required dependencies for this loader are installed as well. See Installation.

_delb.plugins.https_loader.https_loader(data: ~typing.Any, config: ~types.SimpleNamespace, client: ~httpx.Client = <httpx.Client object>) → _delb.typing.LoaderResult

This loader loads a document from a URL with the http and https scheme. Redirects are followed. The default httpx-client follows redirects and can partially be configured with environment variables. The URL will be bound to the name source_url on the document’s Document.config attribute.

Loaders with specifically configured httpx-clients can build on this loader like so:

import httpx
from _delb.plugins import plugin_manager
from _delb.plugins.https_loader import https_loader


client = httpx.Client(follow_redirects=False, trust_env=False)

@plugin_manager.register_loader(before=https_loader)
def custom_https_loader(data, config):
    return https_loader(data, config, client=client)

Parser options

class delb.ParserOptions(cleanup_namespaces: bool = False, collapse_whitespace: bool = False, remove_comments: bool = False, remove_processing_instructions: bool = False, resolve_entities: bool = True, unplugged: bool = False)

The configuration options that define an XML parser’s behaviour.

Parameters

• cleanup_namespaces – Consolidate XML namespace declarations.

• collapse_whitespace – Collapse the content's whitespace.

• remove_comments – Ignore comments.

• remove_processing_instructions – Don’t include processing instructions in the parsed tree.

• resolve_entities – Resolve entities.

• unplugged – Don’t load referenced resources over network.

Nodes

Comment

class delb.CommentNode(etree_element: _Element)

The instances of this class represent comment nodes of a tree.

To instantiate new nodes use new_comment_node().

Properties

content	The comment's text.
depth	The depth (or level) of the node in its tree.
document	The Document instances that the node is associated with or None.
first_child
full_text	The concatenated contents of all text node descendants in document order.
index	The node's index within the parent's collection of child nodes or None when the node has no parent.
last_child
last_descendant
namespaces	The prefix to namespace mapping of the node.
parent	The node's parent or None.

Fetching a single relative node

fetch_following(*filter)	param filter Any number of filter s.
fetch_following_sibling(*filter)	param filter Any number of filter s.
fetch_preceding(*filter)	param filter Any number of filter s.
fetch_preceding_sibling(*filter)	param filter Any number of filter s.

Iterating over relative nodes

iterate_ancestors(*filter)	param filter Any number of filter s that a node must match to be
iterate_children(*filter[, recurse])	A generator iterator that yields nothing.
iterate_descendants(*filter)	param filter Any number of filter s that a node must match to be
iterate_following(*filter)	param filter Any number of filter s that a node must match to be
iterate_following_siblings(*filter)	param filter Any number of filter s that a node must match to be
iterate_preceding(*filter)	param filter Any number of filter s that a node must match to be
iterate_preceding_siblings(*filter)	param filter Any number of filter s that a node must match to be

Querying nodes

xpath(expression[, namespaces])

See Queries with XPath & CSS for details on the extent of the XPath implementation.

Adding nodes

add_following_siblings(*node[, clone])	Adds one or more nodes to the right of the node this method is called on.
add_preceding_siblings(*node[, clone])	Adds one or more nodes to the left of the node this method is called on.

Removing a node from its tree

detach([retain_child_nodes])	Removes the node from its tree.
replace_with(node[, clone])	Removes the node and places the given one in its tree location.

Uncategorized methods

clone([deep, quick_and_unsafe])	param deep Clones the whole subtree if True.
new_tag_node(local_name[, attributes, ...])	Creates a new TagNode instance in the node's context.

---

add_following_siblings(*node: Union[str, NodeBase, _TagDefinition], clone: bool = False)

Adds one or more nodes to the right of the node this method is called on.

The nodes can be concrete instances of any node type or rather abstract descriptions in the form of strings or objects returned from the tag() function that are used to derive TextNode respectively TagNode instances from.

Parameters

• node – The node(s) to be added.

• clone – Clones the concrete nodes before adding if True.

add_preceding_siblings(*node: Union[str, NodeBase, _TagDefinition], clone: bool = False)

Adds one or more nodes to the left of the node this method is called on.

The nodes can be concrete instances of any node type or rather abstract descriptions in the form of strings or objects returned from the tag() function that are used to derive TextNode respectively TagNode instances from.

Parameters

• node – The node(s) to be added.

• clone – Clones the concrete nodes before adding if True.

clone(deep: bool = False, quick_and_unsafe: bool = False) → _ElementWrappingNode

Parameters

• deep – Clones the whole subtree if True.

• quick_and_unsafe – Creates a deep clone in a quicker manner where text nodes may get lost. It should be safe with trees that don’t contain subsequent text nodes, e.g. freshly parsed, unaltered documents of after TagNode.merge_text_nodes() has been applied.

Returns

A copy of the node.

property content: str

The comment’s text.

property depth: int

The depth (or level) of the node in its tree.

detach(retain_child_nodes: bool = False) → _ElementWrappingNode

Removes the node from its tree.

Parameters

retain_child_nodes – Keeps the node’s descendants in the originating tree if True.

Returns

The removed node.

property document: Optional[Document]

The Document instances that the node is associated with or None.

fetch_following(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The next node in document order that matches all filters or None.

fetch_following_sibling(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The next sibling to the right that matches all filters or None.

fetch_preceding(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The previous node in document order that matches all filters or None.

fetch_preceding_sibling(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The next sibling to the left that matches all filters or None.

first_child = None

property full_text: str

The concatenated contents of all text node descendants in document order.

property index: Optional[int]

The node’s index within the parent’s collection of child nodes or None when the node has no parent.

iterate_ancestors(*filter: _delb.typing.Filter) → Iterator[TagNode]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the ancestor nodes from bottom to top.

iterate_children(*filter: _delb.typing.Filter, recurse: bool = False) → Iterator[NodeBase]

A generator iterator that yields nothing.

iterate_descendants(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the descending nodes of the node.

iterate_following(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the following nodes in document order.

iterate_following_siblings(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the siblings to the node’s right.

iterate_preceding(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the previous nodes in document order.

iterate_preceding_siblings(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the siblings to the node’s left.

last_child = None

last_descendant = None

property namespaces: Namespaces

The prefix to namespace mapping of the node.

new_tag_node(local_name: str, attributes: Optional[Dict[str, str]] = None, namespace: Optional[str] = None, children: Sequence[Union[str, NodeBase, _TagDefinition]] = ()) → TagNode

Creates a new TagNode instance in the node’s context.

Parameters

• local_name – The tag name.

• attributes – Optional attributes that are assigned to the new node.

• namespace – An optional tag namespace. If none is provided, the context node’s namespace is inherited.

• children – An optional sequence of objects that will be appended as child nodes. This can be existing nodes, strings that will be inserted as text nodes and in-place definitions of TagNode instances from tag(). The latter will be assigned to the same namespace.

Returns

The newly created tag node.

property parent: Optional[TagNode]

The node’s parent or None.

replace_with(node: Union[str, NodeBase, _TagDefinition], clone: bool = False) → NodeBase

Removes the node and places the given one in its tree location.

The node can be a concrete instance of any node type or a rather abstract description in the form of a string or an object returned from the tag() function that is used to derive a TextNode respectively TagNode instance from.

Parameters

• node – The replacing node.

• clone – A concrete, replacing node is cloned if True.

Returns

The removed node.

xpath(expression: str, namespaces: Optional[Namespaces] = None) → QueryResults

See Queries with XPath & CSS for details on the extent of the XPath implementation.

Parameters

• expression – A supported XPath 1.0 expression that contains one or more location paths.

• namespaces – A mapping of prefixes that are used in the expression to namespaces. If omitted, the node’s definition is used.

Returns

All nodes that match the evaluation of the provided XPath expression.

Processing instruction

class delb.ProcessingInstructionNode(etree_element: _Element)

The instances of this class represent processing instruction nodes of a tree.

To instantiate new nodes use new_processing_instruction_node().

Properties

content	The processing instruction's text.
depth	The depth (or level) of the node in its tree.
document	The Document instances that the node is associated with or None.
first_child
full_text	The concatenated contents of all text node descendants in document order.
index	The node's index within the parent's collection of child nodes or None when the node has no parent.
last_child
last_descendant
namespaces	The prefix to namespace mapping of the node.
parent	The node's parent or None.
target	The processing instruction's target.

Fetching a single relative node

fetch_following(*filter)	param filter Any number of filter s.
fetch_following_sibling(*filter)	param filter Any number of filter s.
fetch_preceding(*filter)	param filter Any number of filter s.
fetch_preceding_sibling(*filter)	param filter Any number of filter s.

Iterating over relative nodes

iterate_ancestors(*filter)	param filter Any number of filter s that a node must match to be
iterate_children(*filter[, recurse])	A generator iterator that yields nothing.
iterate_descendants(*filter)	param filter Any number of filter s that a node must match to be
iterate_following(*filter)	param filter Any number of filter s that a node must match to be
iterate_following_siblings(*filter)	param filter Any number of filter s that a node must match to be
iterate_preceding(*filter)	param filter Any number of filter s that a node must match to be
iterate_preceding_siblings(*filter)	param filter Any number of filter s that a node must match to be

Querying nodes

xpath(expression[, namespaces])

See Queries with XPath & CSS for details on the extent of the XPath implementation.

Adding nodes

add_following_siblings(*node[, clone])	Adds one or more nodes to the right of the node this method is called on.
add_preceding_siblings(*node[, clone])	Adds one or more nodes to the left of the node this method is called on.

Removing a node from its tree

detach([retain_child_nodes])	Removes the node from its tree.
replace_with(node[, clone])	Removes the node and places the given one in its tree location.

Uncategorized methods

clone([deep, quick_and_unsafe])	param deep Clones the whole subtree if True.
new_tag_node(local_name[, attributes, ...])	Creates a new TagNode instance in the node's context.

---

add_following_siblings(*node: Union[str, NodeBase, _TagDefinition], clone: bool = False)

Adds one or more nodes to the right of the node this method is called on.

The nodes can be concrete instances of any node type or rather abstract descriptions in the form of strings or objects returned from the tag() function that are used to derive TextNode respectively TagNode instances from.

Parameters

• node – The node(s) to be added.

• clone – Clones the concrete nodes before adding if True.

add_preceding_siblings(*node: Union[str, NodeBase, _TagDefinition], clone: bool = False)

Adds one or more nodes to the left of the node this method is called on.

The nodes can be concrete instances of any node type or rather abstract descriptions in the form of strings or objects returned from the tag() function that are used to derive TextNode respectively TagNode instances from.

Parameters

• node – The node(s) to be added.

• clone – Clones the concrete nodes before adding if True.

clone(deep: bool = False, quick_and_unsafe: bool = False) → _ElementWrappingNode

Parameters

• deep – Clones the whole subtree if True.

• quick_and_unsafe – Creates a deep clone in a quicker manner where text nodes may get lost. It should be safe with trees that don’t contain subsequent text nodes, e.g. freshly parsed, unaltered documents of after TagNode.merge_text_nodes() has been applied.

Returns

A copy of the node.

property content: str

The processing instruction’s text.

property depth: int

The depth (or level) of the node in its tree.

detach(retain_child_nodes: bool = False) → _ElementWrappingNode

Removes the node from its tree.

Parameters

retain_child_nodes – Keeps the node’s descendants in the originating tree if True.

Returns

The removed node.

property document: Optional[Document]

The Document instances that the node is associated with or None.

fetch_following(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The next node in document order that matches all filters or None.

fetch_following_sibling(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The next sibling to the right that matches all filters or None.

fetch_preceding(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The previous node in document order that matches all filters or None.

fetch_preceding_sibling(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The next sibling to the left that matches all filters or None.

first_child = None

property full_text: str

The concatenated contents of all text node descendants in document order.

property index: Optional[int]

The node’s index within the parent’s collection of child nodes or None when the node has no parent.

iterate_ancestors(*filter: _delb.typing.Filter) → Iterator[TagNode]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the ancestor nodes from bottom to top.

iterate_children(*filter: _delb.typing.Filter, recurse: bool = False) → Iterator[NodeBase]

A generator iterator that yields nothing.

iterate_descendants(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the descending nodes of the node.

iterate_following(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the following nodes in document order.

iterate_following_siblings(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the siblings to the node’s right.

iterate_preceding(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the previous nodes in document order.

iterate_preceding_siblings(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the siblings to the node’s left.

last_child = None

last_descendant = None

property namespaces: Namespaces

The prefix to namespace mapping of the node.

new_tag_node(local_name: str, attributes: Optional[Dict[str, str]] = None, namespace: Optional[str] = None, children: Sequence[Union[str, NodeBase, _TagDefinition]] = ()) → TagNode

Creates a new TagNode instance in the node’s context.

Parameters

• local_name – The tag name.

• attributes – Optional attributes that are assigned to the new node.

• namespace – An optional tag namespace. If none is provided, the context node’s namespace is inherited.

• children – An optional sequence of objects that will be appended as child nodes. This can be existing nodes, strings that will be inserted as text nodes and in-place definitions of TagNode instances from tag(). The latter will be assigned to the same namespace.

Returns

The newly created tag node.

property parent: Optional[TagNode]

The node’s parent or None.

replace_with(node: Union[str, NodeBase, _TagDefinition], clone: bool = False) → NodeBase

Removes the node and places the given one in its tree location.

The node can be a concrete instance of any node type or a rather abstract description in the form of a string or an object returned from the tag() function that is used to derive a TextNode respectively TagNode instance from.

Parameters

• node – The replacing node.

• clone – A concrete, replacing node is cloned if True.

Returns

The removed node.

property target: str

The processing instruction’s target.

xpath(expression: str, namespaces: Optional[Namespaces] = None) → QueryResults

See Queries with XPath & CSS for details on the extent of the XPath implementation.

Parameters

• expression – A supported XPath 1.0 expression that contains one or more location paths.

• namespaces – A mapping of prefixes that are used in the expression to namespaces. If omitted, the node’s definition is used.

Returns

All nodes that match the evaluation of the provided XPath expression.

Tag

class delb.TagNode(etree_element: _Element)

The instances of this class represent tag node s of a tree, the equivalent of DOM’s elements.

To instantiate new nodes use Document.new_tag_node, TagNode.new_tag_node, TextNode.new_tag_node or new_tag_node().

Some syntactic sugar is baked in:

Attributes and nodes can be tested for membership in a node.

>>> root = Document('<root ham="spam"><child/></root>').root
>>> child = root.first_child
>>> "ham" in root
True
>>> child in root
True

Nodes can be copied. Note that this relies on TagNode.clone().

>>> from copy import copy, deepcopy
>>> root = Document("<root>Content</root>").root
>>> print(copy(root))
<root/>
>>> print(deepcopy(root))
<root>Content</root>

Nodes can be tested for equality regarding their qualified name and attributes.

>>> root = Document('<root><foo x="0"/><foo x="0"/><bar x="0"/></root>').root
>>> root[0] == root[1]
True
>>> root[0] == root[2]
False

Attribute values and child nodes can be obtained with the subscript notation.

>>> root = Document('<root x="0"><child_1/>child_2<child_3/></root>').root
>>> root["x"]
'0'
>>> print(root[0])
<child_1/>
>>> print(root[-1])
<child_3/>
>>> print([str(x) for x in root[1::-1]])
['child_2', '<child_1/>']

How much child nodes has this node anyway?

>>> root = Document("<root><child_1/><child_2/></root>").root
>>> len(root)
2
>>> len(root[0])
0

As seen in the examples above, a tag nodes string representation yields a serialized XML representation of a sub-/tree.

Properties

attributes	A mapping that can be used to query and alter the node's attributes.
depth	The depth (or level) of the node in its tree.
document	The Document instances that the node is associated with or None.
first_child	The node's first child node.
full_text	The concatenated contents of all text node descendants in document order.
id	This is a shortcut to retrieve and set the id attribute in the XML namespace.
index	The node's index within the parent's collection of child nodes or None when the node has no parent.
last_child	The node's last child node.
last_descendant	The node's last descendant.
local_name	The node's name.
location_path	An unambiguous XPath location path that points to this node from its tree root.
namespace	The node's namespace.
namespaces	The prefix to namespace mapping of the node.
parent	The node's parent or None.
prefix	The prefix that the node's namespace is currently mapped to.
universal_name	The node's qualified name in Clark notation.

Fetching a single relative node

fetch_following(*filter)	param filter Any number of filter s.
fetch_following_sibling(*filter)	param filter Any number of filter s.
fetch_preceding(*filter)	param filter Any number of filter s.
fetch_preceding_sibling(*filter)	param filter Any number of filter s.

Iterating over relative nodes

iterate_ancestors(*filter)	param filter Any number of filter s that a node must match to be
iterate_children(*filter[, recurse])	param filter Any number of filter s that a node must match to be
iterate_descendants(*filter)	param filter Any number of filter s that a node must match to be
iterate_following(*filter)	param filter Any number of filter s that a node must match to be
iterate_following_siblings(*filter)	param filter Any number of filter s that a node must match to be
iterate_preceding(*filter)	param filter Any number of filter s that a node must match to be
iterate_preceding_siblings(*filter)	param filter Any number of filter s that a node must match to be

Querying nodes

css_select(expression[, namespaces])	See Queries with XPath & CSS regarding the extent of the supported grammar.
fetch_or_create_by_xpath(expression[, ...])	Fetches a single node that is locatable by the provided XPath expression.
xpath(expression[, namespaces])	See Queries with XPath & CSS for details on the extent of the XPath implementation.

Adding nodes

add_following_siblings(*node[, clone])	Adds one or more nodes to the right of the node this method is called on.
add_preceding_siblings(*node[, clone])	Adds one or more nodes to the left of the node this method is called on.
append_children(*node[, clone])	Adds one or more nodes as child nodes after any existing to the child nodes of the node this method is called on.
insert_children(index, *node[, clone])	Inserts one or more child nodes.
prepend_children(*node[, clone])	Adds one or more nodes as child nodes before any existing to the child nodes of the node this method is called on.

Removing a node from its tree

detach([retain_child_nodes])	Removes the node from its tree.
replace_with(node[, clone])	Removes the node and places the given one in its tree location.

Uncategorized methods

clone([deep, quick_and_unsafe])	param deep Clones the whole subtree if True.
merge_text_nodes()	Merges all consecutive text nodes in the subtree into one.
new_tag_node(local_name[, attributes, ...])	Creates a new TagNode instance in the node's context.
parse(text[, parser, parser_options, ...])	Parses the given string or bytes sequence into a new tree.

---

add_following_siblings(*node: Union[str, NodeBase, _TagDefinition], clone: bool = False)

Adds one or more nodes to the right of the node this method is called on.

The nodes can be concrete instances of any node type or rather abstract descriptions in the form of strings or objects returned from the tag() function that are used to derive TextNode respectively TagNode instances from.

Parameters

• node – The node(s) to be added.

• clone – Clones the concrete nodes before adding if True.

add_preceding_siblings(*node: Union[str, NodeBase, _TagDefinition], clone: bool = False)

Adds one or more nodes to the left of the node this method is called on.

The nodes can be concrete instances of any node type or rather abstract descriptions in the form of strings or objects returned from the tag() function that are used to derive TextNode respectively TagNode instances from.

Parameters

• node – The node(s) to be added.

• clone – Clones the concrete nodes before adding if True.

append_children(*node: Union[str, NodeBase, _TagDefinition], clone: bool = False)

Adds one or more nodes as child nodes after any existing to the child nodes of the node this method is called on.

The nodes can be concrete instances of any node type or rather abstract descriptions in the form of strings or objects returned from the tag() function that are used to derive TextNode respectively TagNode instances from.

Parameters

• node – The node(s) to be added.

• clone – Clones the concrete nodes before adding if True.

property attributes: TagAttributes

A mapping that can be used to query and alter the node’s attributes.

>>> node = new_tag_node("node", attributes={"foo": "0", "bar": "0"})
>>> node.attributes
{'foo': '0', 'bar': '0'}
>>> node.attributes.pop("bar")
'0'
>>> node.attributes["foo"] = "1"
>>> node.attributes["peng"] = "1"
>>> print(node)
<node foo="1" peng="1"/>
>>> node.attributes.update({"foo": "2", "zong": "2"})
>>> print(node)
<node foo="2" peng="1" zong="2"/>

Namespaced attributes can be accessed by using Python’s slice notation. A default namespace can be provided optionally, but it’s also found without.

>>> node = new_tag_node("node", {})
>>> node.attributes["http://namespace":"foo"] = "0"
>>> print(node)
<node xmlns:ns0="http://namespace" ns0:foo="0"/>
>>> node = Document('<node xmlns="default" foo="0"/>').root
>>> node.attributes["default":"foo"] is node.attributes["foo"]
True

Attributes behave like strings, but also expose namespace, local name and value for manipulation.

>>> node = new_tag_node("node")
>>> node.attributes["foo"] = "0"
>>> node.attributes["foo"].local_name = "bar"
>>> node.attributes["bar"].namespace = "http://namespace"
>>> node.attributes["http://namespace":"bar"].value = "1"
>>> print(node)
<node xmlns:ns0="http://namespace" ns0:bar="1"/>

Unlike with typical Python mappings, requesting a non-existing attribute doesn’t evoke a KeyError, instead None is returned.

clone(deep: bool = False, quick_and_unsafe: bool = False) → TagNode

Parameters

• deep – Clones the whole subtree if True.

• quick_and_unsafe – Creates a deep clone in a quicker manner where text nodes may get lost. It should be safe with trees that don’t contain subsequent text nodes, e.g. freshly parsed, unaltered documents of after TagNode.merge_text_nodes() has been applied.

Returns

A copy of the node.

css_select(expression: str, namespaces: Optional[Namespaces] = None) → QueryResults

See Queries with XPath & CSS regarding the extent of the supported grammar.

Namespace prefixes are delimited with a | before a name test, for example div svg|metadata selects all descendants of div named nodes that belong to the default namespace or have no namespace and whose name is metadata and have a namespace that is mapped to the svg prefix.

Parameters

• expression – A CSS selector expression.

• namespaces – A mapping of prefixes that are used in the expression to namespaces. If omitted, the node’s definition is used.

Returns

All nodes that match the evaluation of the provided CSS selector expression.

property depth: int

The depth (or level) of the node in its tree.

detach(retain_child_nodes: bool = False) → _ElementWrappingNode

Removes the node from its tree.

Parameters

retain_child_nodes – Keeps the node’s descendants in the originating tree if True.

Returns

The removed node.

property document: Optional[Document]

The Document instances that the node is associated with or None.

fetch_following(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The next node in document order that matches all filters or None.

fetch_following_sibling(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The next sibling to the right that matches all filters or None.

fetch_or_create_by_xpath(expression: str, namespaces: Union[Namespaces, None, Mapping[Optional[str], str]] = None) → TagNode

Fetches a single node that is locatable by the provided XPath expression. If the node doesn’t exist, the non-existing branch will be created. These rules are imperative in your endeavour:

• All location steps must use the child axis.

• Each step needs to provide a name test.

• Attributes must be compared against a literal.

• Multiple attribute comparisons must be joined with the and operator and / or more than one predicate expression.

• The logical validity of multiple attribute comparisons isn’t checked. E.g. one could provide foo[@p="her"][@p="him"], but expect an undefined behaviour.

• Other contents in predicate expressions are invalid.

>>> document = Document("<root/>")
>>> grandchild = document.root.fetch_or_create_by_xpath(
...     "child[@a='b']/grandchild"
... )
>>> grandchild is document.root.fetch_or_create_by_xpath(
...     "child[@a='b']/grandchild"
... )
True
>>> str(document)
'<root><child a="b"><grandchild/></child></root>'

Parameters

• expression – An XPath expression that can unambiguously locate a descending node in a tree that has any state.

• namespaces – An optional mapping of prefixes to namespaces. As default the node’s one is used.

Returns

The existing or freshly created node descibed with expression.

fetch_preceding(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The previous node in document order that matches all filters or None.

fetch_preceding_sibling(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The next sibling to the left that matches all filters or None.

property first_child: Optional[NodeBase]

The node’s first child node.

property full_text: str

The concatenated contents of all text node descendants in document order.

property id: Optional[str]

This is a shortcut to retrieve and set the id attribute in the XML namespace. The client code is responsible to pass properly formed id names.

property index: Optional[int]

The node’s index within the parent’s collection of child nodes or None when the node has no parent.

insert_children(index: int, *node: Union[str, NodeBase, _TagDefinition], clone: bool = False)

Inserts one or more child nodes.

The nodes can be concrete instances of any node type or rather abstract descriptions in the form of strings or objects returned from the tag() function that are used to derive TextNode respectively TagNode instances from.

Parameters

• index – The index at which the first of the given nodes will be inserted, the remaining nodes are added afterwards in the given order.

• node – The node(s) to be added.

• clone – Clones the concrete nodes before adding if True.

iterate_ancestors(*filter: _delb.typing.Filter) → Iterator[TagNode]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the ancestor nodes from bottom to top.

iterate_children(*filter: _delb.typing.Filter, recurse: bool = False) → Iterator[NodeBase]

Parameters

• filter – Any number of filter s that a node must match to be yielded.

• recurse – Deprecated. Use NodeBase.iterate_descendants().

Returns

A generator iterator that yields the child nodes of the node.

iterate_descendants(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the descending nodes of the node.

iterate_following(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the following nodes in document order.

iterate_following_siblings(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the siblings to the node’s right.

iterate_preceding(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the previous nodes in document order.

iterate_preceding_siblings(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the siblings to the node’s left.

property last_child: Optional[NodeBase]

The node’s last child node.

property last_descendant: Optional[NodeBase]

The node’s last descendant.

property local_name: str

The node’s name.

property location_path: str

An unambiguous XPath location path that points to this node from its tree root.

merge_text_nodes()

Merges all consecutive text nodes in the subtree into one.

property namespace: Optional[str]

The node’s namespace. Be aware, that while this property can be set to None, serializations will continue to render a previous default namespace declaration if the node had such.

property namespaces: Namespaces

The prefix to namespace mapping of the node.

new_tag_node(local_name: str, attributes: Optional[Dict[str, str]] = None, namespace: Optional[str] = None, children: Sequence[Union[str, NodeBase, _TagDefinition]] = ()) → TagNode

Creates a new TagNode instance in the node’s context.

Parameters

• local_name – The tag name.

• attributes – Optional attributes that are assigned to the new node.

• namespace – An optional tag namespace. If none is provided, the context node’s namespace is inherited.

• children – An optional sequence of objects that will be appended as child nodes. This can be existing nodes, strings that will be inserted as text nodes and in-place definitions of TagNode instances from tag(). The latter will be assigned to the same namespace.

Returns

The newly created tag node.

property parent: Optional[TagNode]

The node’s parent or None.

static parse(text: AnyStr, parser: Optional[XMLParser] = None, parser_options: Optional[ParserOptions] = None, collapse_whitespace: Optional[bool] = None) → TagNode

Parses the given string or bytes sequence into a new tree.

Parameters

• text – A serialized XML tree.

• parser – Deprecated.

• parser_options – A delb.ParserOptions class to configure the used parser.

• collapse_whitespace – Deprecated. Use the argument with the same name on the parser_options object.

property prefix: Optional[str]

The prefix that the node’s namespace is currently mapped to.

prepend_children(*node: NodeBase, clone: bool = False) → None

Adds one or more nodes as child nodes before any existing to the child nodes of the node this method is called on.

The nodes can be concrete instances of any node type or rather abstract descriptions in the form of strings or objects returned from the tag() function that are used to derive TextNode respectively TagNode instances from.

Parameters

• node – The node(s) to be added.

• clone – Clones the concrete nodes before adding if True.

replace_with(node: Union[str, NodeBase, _TagDefinition], clone: bool = False) → NodeBase

Removes the node and places the given one in its tree location.

The node can be a concrete instance of any node type or a rather abstract description in the form of a string or an object returned from the tag() function that is used to derive a TextNode respectively TagNode instance from.

Parameters

• node – The replacing node.

• clone – A concrete, replacing node is cloned if True.

Returns

The removed node.

property universal_name: str

The node’s qualified name in Clark notation.

xpath(expression: str, namespaces: Optional[Namespaces] = None) → QueryResults

See Queries with XPath & CSS for details on the extent of the XPath implementation.

Parameters

• expression – A supported XPath 1.0 expression that contains one or more location paths.

• namespaces – A mapping of prefixes that are used in the expression to namespaces. If omitted, the node’s definition is used.

Returns

All nodes that match the evaluation of the provided XPath expression.

Tag attribute

class delb.nodes.Attribute(attributes: TagAttributes, key: str)

Attribute objects represent tag node’s attributes. See the delb.TagNode.attributes() documentation for capabilities.

property local_name: str

The attribute’s local name.

property namespace: Optional[str]

The attribute’s namespace

property universal_name: str

The attribute’s namespace and local name in Clark notation.

property value: str

The attribute’s value.

Text

class delb.TextNode(reference_or_text: Union[_Element, str, TextNode], position: int = 0)

TextNodes contain the textual data of a document. The class shall not be initialized by client code, just throw strings into the trees.

Instances expose all methods of str except str.index():

>>> node = TextNode("Show us the way to the next whisky bar.")
>>> node.split()
['Show', 'us', 'the', 'way', 'to', 'the', 'next', 'whisky', 'bar.']

Instances can be tested for inequality with other text nodes and strings:

>>> TextNode("ham") == TextNode("spam")
False
>>> TextNode("Patsy") == "Patsy"
True

And they can be tested for substrings:

>>> "Sir" in TextNode("Sir Bedevere the Wise")
True

Attributes that rely to child nodes yield nothing respectively None.

Properties

content	The node's text content.
depth	The depth (or level) of the node in its tree.
document	The Document instances that the node is associated with or None.
first_child
full_text	The concatenated contents of all text node descendants in document order.
index	The node's index within the parent's collection of child nodes or None when the node has no parent.
last_child
last_descendant
namespaces	The prefix to namespace mapping of the node.
parent	The node's parent or None.

Fetching a single relative node

fetch_following(*filter)	param filter Any number of filter s.
fetch_following_sibling(*filter)	param filter Any number of filter s.
fetch_preceding(*filter)	param filter Any number of filter s.
fetch_preceding_sibling(*filter)	param filter Any number of filter s.

Iterating over relative nodes

iterate_ancestors(*filter)	param filter Any number of filter s that a node must match to be
iterate_children(*filter[, recurse])	A generator iterator that yields nothing.
iterate_descendants(*filter)	param filter Any number of filter s that a node must match to be
iterate_following(*filter)	param filter Any number of filter s that a node must match to be
iterate_following_siblings(*filter)	param filter Any number of filter s that a node must match to be
iterate_preceding(*filter)	param filter Any number of filter s that a node must match to be
iterate_preceding_siblings(*filter)	param filter Any number of filter s that a node must match to be

Querying nodes

xpath(expression[, namespaces])

See Queries with XPath & CSS for details on the extent of the XPath implementation.

Adding nodes

add_following_siblings(*node[, clone])	Adds one or more nodes to the right of the node this method is called on.
add_preceding_siblings(*node[, clone])	Adds one or more nodes to the left of the node this method is called on.

Removing a node from its tree

detach([retain_child_nodes])	Removes the node from its tree.
replace_with(node[, clone])	Removes the node and places the given one in its tree location.

Uncategorized methods

clone([deep, quick_and_unsafe])	param deep Clones the whole subtree if True.
new_tag_node(local_name[, attributes, ...])	Creates a new TagNode instance in the node's context.

---

add_following_siblings(*node: Union[str, NodeBase, _TagDefinition], clone: bool = False)

Adds one or more nodes to the right of the node this method is called on.

The nodes can be concrete instances of any node type or rather abstract descriptions in the form of strings or objects returned from the tag() function that are used to derive TextNode respectively TagNode instances from.

Parameters

• node – The node(s) to be added.

• clone – Clones the concrete nodes before adding if True.

add_preceding_siblings(*node: Union[str, NodeBase, _TagDefinition], clone: bool = False)

Adds one or more nodes to the left of the node this method is called on.

The nodes can be concrete instances of any node type or rather abstract descriptions in the form of strings or objects returned from the tag() function that are used to derive TextNode respectively TagNode instances from.

Parameters

• node – The node(s) to be added.

• clone – Clones the concrete nodes before adding if True.

clone(deep: bool = False, quick_and_unsafe: bool = False) → NodeBase

Parameters

• deep – Clones the whole subtree if True.

• quick_and_unsafe – Creates a deep clone in a quicker manner where text nodes may get lost. It should be safe with trees that don’t contain subsequent text nodes, e.g. freshly parsed, unaltered documents of after TagNode.merge_text_nodes() has been applied.

Returns

A copy of the node.

property content: str

The node’s text content.

property depth: int

The depth (or level) of the node in its tree.

detach(retain_child_nodes: bool = False) → TextNode

Removes the node from its tree.

Parameters

retain_child_nodes – Keeps the node’s descendants in the originating tree if True.

Returns

The removed node.

property document: Optional[Document]

The Document instances that the node is associated with or None.

fetch_following(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The next node in document order that matches all filters or None.

fetch_following_sibling(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The next sibling to the right that matches all filters or None.

fetch_preceding(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The previous node in document order that matches all filters or None.

fetch_preceding_sibling(*filter: _delb.typing.Filter) → Optional[NodeBase]

Parameters

filter – Any number of filter s.

Returns

The next sibling to the left that matches all filters or None.

first_child = None

property full_text: str

The concatenated contents of all text node descendants in document order.

property index: Optional[int]

The node’s index within the parent’s collection of child nodes or None when the node has no parent.

iterate_ancestors(*filter: _delb.typing.Filter) → Iterator[TagNode]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the ancestor nodes from bottom to top.

iterate_children(*filter: _delb.typing.Filter, recurse: bool = False) → Iterator[NodeBase]

A generator iterator that yields nothing.

iterate_descendants(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the descending nodes of the node.

iterate_following(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the following nodes in document order.

iterate_following_siblings(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the siblings to the node’s right.

iterate_preceding(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the previous nodes in document order.

iterate_preceding_siblings(*filter: _delb.typing.Filter) → Iterator[NodeBase]

Parameters

filter – Any number of filter s that a node must match to be yielded.

Returns

A generator iterator that yields the siblings to the node’s left.

last_child = None

last_descendant = None

property namespaces

The prefix to namespace mapping of the node.

new_tag_node(local_name: str, attributes: Optional[Dict[str, str]] = None, namespace: Optional[str] = None, children: Sequence[Union[str, NodeBase, _TagDefinition]] = ()) → TagNode

Creates a new TagNode instance in the node’s context.

Parameters

• local_name – The tag name.

• attributes – Optional attributes that are assigned to the new node.

• namespace – An optional tag namespace. If none is provided, the context node’s namespace is inherited.

• children – An optional sequence of objects that will be appended as child nodes. This can be existing nodes, strings that will be inserted as text nodes and in-place definitions of TagNode instances from tag(). The latter will be assigned to the same namespace.

Returns

The newly created tag node.

property parent: Optional[TagNode]

The node’s parent or None.

replace_with(node: Union[str, NodeBase, _TagDefinition], clone: bool = False) → NodeBase

Removes the node and places the given one in its tree location.

The node can be a concrete instance of any node type or a rather abstract description in the form of a string or an object returned from the tag() function that is used to derive a TextNode respectively TagNode instance from.

Parameters

• node – The replacing node.

• clone – A concrete, replacing node is cloned if True.

Returns

The removed node.

xpath(expression: str, namespaces: Optional[Namespaces] = None) → QueryResults

See Queries with XPath & CSS for details on the extent of the XPath implementation.

Parameters

• expression – A supported XPath 1.0 expression that contains one or more location paths.

• namespaces – A mapping of prefixes that are used in the expression to namespaces. If omitted, the node’s definition is used.

Returns

All nodes that match the evaluation of the provided XPath expression.

Node constructors

delb.new_comment_node(content: str) → CommentNode

Creates a new CommentNode.

Parameters

content – The comment’s content a.k.a. as text.

Returns

The newly created comment node.

delb.new_processing_instruction_node(target: str, content: str) → ProcessingInstructionNode

Creates a new ProcessingInstructionNode.

Parameters

• target – The processing instruction’s target name.

• content – The processing instruction’s text.

Returns

The newly created processing instruction node.

delb.new_tag_node(local_name: str, attributes: Optional[Dict[str, str]] = None, namespace: Optional[str] = None, children: Sequence[Union[str, NodeBase, _TagDefinition]] = ()) → TagNode

Creates a new TagNode instance outside any context. It is preferable to use new_tag_node(), on instances of documents and nodes where the instance is the creation context.

Parameters

• local_name – The tag name.

• attributes – Optional attributes that are assigned to the new node.

• namespace – An optional tag namespace.

• children – An optional sequence of objects that will be appended as child nodes. This can be existing nodes, strings that will be inserted as text nodes and in-place definitions of TagNode instances from tag(). The latter will be assigned to the same namespace.

Returns

The newly created tag node.

Queries with XPath & CSS

delb allows querying of nodes with CSS selector and XPath expressions. CSS selectors are converted to XPath expressions with a third-party library before evaluation and they are only supported as far as their computed XPath equivalents are supported by delb’s very own XPath implementation.

This implementation is not fully compliant with one of the W3C’s XPath specifications. It mostly covers the XPath 1.0 specs, but focuses on the querying via path expressions with simple constraints while it omits a broad employment of computations (that’s what programming languages are for) and has therefore these intended deviations from that standard:

• Default namespaces can be addressed in node and attribute names, by simply using no prefix.

• The attribute and namespace axes are not supported in location steps (see also below).

• In predicates only the attribute axis can be used in its abbreviated form (@name).

• Path evaluations within predicates are not available.

• Only these predicate functions are provided and tested:

  • boolean

  • concat

  • contains

  • last

  • not

  • position

  • starts-with

  • text

    • Behaves as if deployed as a single step location path that only tests for the node type text. Hence it returns the contents of the context node’s first child node that is a text node or an empty string when there is none.

  • Please refrain from extension requests without a proper, concrete implementation proposal.

If you’re accustomed to retrieve attribute values with XPath expressions, employ the functionality of the higher programming language at hand like this:

>>> [x.attributes["target"] for x in root.xpath(".//foo")
...  if "target" in x.attributes ]  

Instead of:

>>> root.xpath(".//foo/@target")  

See _delb.plugins.PluginManager.register_xpath_function() regarding the use of custom functions.

class _delb.xpath.EvaluationContext(node: NodeBase, position: int, size: int, namespaces: Namespaces)

Instances of this type are passed to XPath functions in order to pass contextual information.

count(value, /)

Return number of occurrences of value.

index(value, start=0, stop=9223372036854775807, /)

Return first index of value.

Raises ValueError if the value is not present.

property namespaces

A mapping of prefixes to namespaces that is used in the whole evaluation.

property node

The node that is evaluated.

property position

The node’s position within all nodes that matched a location step’s node test in order of the step’s axis’ direction. The first position is 1.

property size

The number of all nodes all nodes that matched a location step’s node test.

class _delb.xpath.QueryResults(results: Iterable[NodeBase])

A container that includes the results of a CSS selector or XPath query with some helpers for better readable Python expressions.

as_list() → List[NodeBase]

The contained nodes as a new list.

property as_tuple: Tuple[NodeBase, ...]

The contained nodes in a tuple.

count(value) → integer -- return number of occurrences of value

filtered_by(*filters: _delb.typing.Filter) → QueryResults

Returns another QueryResults instance that contains all nodes filtered by the provided filter s.

property first: Optional[NodeBase]

The first node from the results or None if there are none.

in_document_order() → QueryResults

Returns another QueryResults instance where the contained nodes are sorted in document order.

index(value[, start[, stop]]) → integer -- return first index of value.

Raises ValueError if the value is not present.

Supporting start and stop arguments is optional, but recommended.

property last: Optional[NodeBase]

The last node from the results or None if there are none.

property size: int

The amount of contained nodes.

Filters

Default filters

delb.altered_default_filters(*filter: _delb.typing.Filter, extend: bool = False)

This function can be either used as as context manager or decorator to define a set of default_filters for the encapsuled code block or callable. These are then applied in all operations that allow node filtering, like TagNode.next_node(). Mind that they also affect a node’s index property and indexed access to child nodes.

>>> root = Document(
...     '<root xmlns="foo"><a/><!--x--><b/><!--y--><c/></root>'
... ).root
>>> with altered_default_filters(is_comment_node):
...     print([x.content for x in root.iterate_children()])
['x', 'y']

As the default filters shadow comments and processing instructions by default, use no argument to unset this in order to access all type of nodes.

Parameters

extend – Extends the currently active filters with the given ones instead of replacing them.

Contributed filters

delb.any_of(*filter: _delb.typing.Filter) → _delb.typing.Filter

A node filter wrapper that matches when any of the given filters is matching, like a boolean or.

delb.is_comment_node(node: NodeBase) → bool

A node filter that matches CommentNode instances.

delb.is_processing_instruction_node(node: NodeBase) → bool

A node filter that matches ProcessingInstructionNode instances.

delb.is_tag_node(node: NodeBase) → bool

A node filter that matches TagNode instances.

delb.is_text_node(node: NodeBase) → bool

A node filter that matches TextNode instances.

delb.not_(*filter: _delb.typing.Filter) → _delb.typing.Filter

A node filter wrapper that matches when the given filter is not matching, like a boolean not.

Transformations

This module offers a canonical interface with the aim to make re-use of transforming algorithms easier.

Let’s look at it with examples:

from delb.transform import Transformation


class ResolveCopyOf(Transformation):
    def transform(self):
        for node in self.root.css_select("*[copyOf]"):
            source_id = node["copyOf"]
            source_node = self.origin_document.xpath(
                f'//*[@xml:id="{source_id[1:]}"]'
            ).first
            cloned_node = source_node.clone(deep=True)
            cloned_node.id = None
            node.replace_with(cloned_node)

From such defined transformations instances can be called with a (sub-)tree and an optional document where that tree originates from:

resolve_copy_of = ResolveCopyOf()
tree = resolve_copy_of(tree)  # where tree is an instance of TagNode

typing.NamedTuple are used to define options for transformations:

from typing import NamedTuple


class ResolveChoiceOptions(NamedTuple):
    corr: bool = True
    reg: bool = True


class ResolveChoice(Transformation):
    options_class = ResolveChoiceOptions

    def __init__(self, options):
        super().__init__(options)
        self.keep_selector = ",".join(
            (
                "corr" if self.options.corr else "sic",
                "reg" if self.options.reg else "orig"
            )
         )
        self.drop_selector = ",".join(
            (
                "sic" if self.options.corr else "corr",
                "orig" if self.options.reg else "reg"
            )
        )

    def transform(self):
        for choice_node in self.root.css_select("choice"):
            node_to_drop = choice_node.css_select(self.drop_selector).first
            node_to_drop.detach()

            node_to_keep = choice_node.css_select(self.keep_selector).first
            node_to_keep.detach(retain_child_nodes=True)

            choice_node.detach(retain_child_nodes=True)

A transformation class that defines an option_class property can then either be used with its defaults or with alternate options:

resolve_choice = ResolveChoice()
tree = resolve_choice(tree)

resolve_choice = ResolveChoice(ResolveChoiceOptions(reg=False))
tree = resolve_choice(tree)

Finally, concrete transformations can be chained, both as classes or instances. The interface allows also to chain multiple chains:

from delb.transform import TransformationSequence

tidy_up = TransformationSequence(ResolveCopyOf, resolve_choice)
tree = tidy_up(tree)

Attention

This is an experimental feature. It might change significantly in the future or be removed altogether.

class delb.transform.Transformation(options: Optional[NamedTuple] = None)

This is a base class for any transformation algorithm.

abstract transform()

This method needs to implement the transformation logic. When it is called, the instance has two attributes assigned from its call:

root is the node that the transformation was called to transform with. origin_document is the document that was possibly passed as second argument.

class delb.transform.TransformationBase

This base class defines the calling interface of transformations.

class delb.transform.TransformationSequence(*transformations: Union[TransformationBase, Type[TransformationBase]])

A transformation sequence can be used to combine any number of both Transformation (provided as class or instantiated with options) and other TransformationSequence instances or classes.

Various helpers

delb.first(iterable: Iterable) → Optional[Any]

Returns the first item of the given iterable or None if it’s empty. Note that the first item is consumed when the iterable is an iterator.

delb.get_traverser(from_left=True, depth_first=True, from_top=True)

Returns a function that can be used to traverse a (sub)tree with the given node as root. While traversing the given root node is yielded at some point.

The returned functions have this signature:

def traverser(root: NodeBase, *filters: Filter) -> Iterator[NodeBase]:
    ...

Parameters

• from_left – The traverser yields sibling nodes from left to right if True, or starting from the right if False.

• depth_first – The child nodes resp. the parent node are yielded before the siblings of a node by a traverser if True. Siblings are favored if False.

• from_top – The traverser starts yielding nodes with the lowest depth if True. When False, again, the opposite is in effect.

delb.last(iterable: Iterable) → Optional[Any]

Returns the last item of the given iterable or None if it’s empty. Note that the whole iterator is consumed when such is given.

delb.register_namespace(prefix: str, namespace: str)

Registers a namespace prefix that newly created TagNode instances in that namespace will use in serializations.

The registry is global, and any existing mapping for either the given prefix or the namespace URI will be removed. It has however no effect on the serialization of existing nodes, see Document.cleanup_namespace() for that.

Parameters

• prefix – The prefix to register.

• namespace – The targeted namespace.

delb.tag(local_name: str)

delb.tag(local_name: str, attributes: Mapping[str, str])

delb.tag(local_name: str, child: Union[str, NodeBase, _TagDefinition])

delb.tag(local_name: str, children: Sequence[Union[str, NodeBase, _TagDefinition]])

delb.tag(local_name: str, attributes: Mapping[str, str], child: Union[str, NodeBase, _TagDefinition])

delb.tag(local_name: str, attributes: Mapping[str, str], children: Sequence[Union[str, NodeBase, _TagDefinition]])

This function can be used for in-place creation (or call it templating if you want to) of TagNode instances as:

• node argument to methods that add nodes to a tree

• items in the children argument of new_tag_node() and NodeBase.new_tag_node()

The first argument to the function is always the local name of the tag node. Optionally, the second argument can be a mapping that specifies attributes for that node. The optional last argument is either a single object that will be appended as child node or a sequence of such, these objects can be node instances of any type, strings (for derived TextNode instances) or other definitions from this function (for derived TagNode instances).

The actual nodes that are constructed always inherit the namespace of the context node they are created in.

>>> root = new_tag_node('root', children=[
...     tag("head", {"lvl": "1"}, "Hello!"),
...     tag("items", (
...         tag("item1"),
...         tag("item2"),
...         )
...     )
... ])
>>> str(root)
'<root><head lvl="1">Hello!</head><items><item1/><item2/></items></root>'
>>> root.append_children(tag("addendum"))
>>> str(root)[-26:]
'</items><addendum/></root>'

Exceptions

exception delb.exceptions.AmbiguousTreeError(message: str)

Raised when a single node shall be fetched or created by an XPath expression in a tree where the target position can’t be clearly determined.

with_traceback()

Exception.with_traceback(tb) – set self.__traceback__ to tb and return self.

exception delb.exceptions.DelbBaseException

with_traceback()

Exception.with_traceback(tb) – set self.__traceback__ to tb and return self.

exception delb.exceptions.FailedDocumentLoading(source: Any, excuses: Dict[Callable[[Any, SimpleNamespace], Union[_ElementTree, str]], Union[str, Exception]])

with_traceback()

Exception.with_traceback(tb) – set self.__traceback__ to tb and return self.

exception delb.exceptions.InvalidCodePath

Raised when a code path that is not expected to be executed is reached.

with_traceback()

Exception.with_traceback(tb) – set self.__traceback__ to tb and return self.

exception delb.exceptions.InvalidOperation

Raised when an invalid operation is attempted by the client code.

with_traceback()

Exception.with_traceback(tb) – set self.__traceback__ to tb and return self.

exception delb.exceptions.XPathEvaluationError(message: str)

with_traceback()

Exception.with_traceback(tb) – set self.__traceback__ to tb and return self.

exception delb.exceptions.XPathParsingError(expression: Optional[str] = None, position: Optional[int] = None, message: Optional[str] = None)

Raised when an XPath expression can’t be parsed.

with_traceback()

Exception.with_traceback(tb) – set self.__traceback__ to tb and return self.

exception delb.exceptions.XPathUnsupportedStandardFeature(position: int, feature_description: str)

Raised when an unsupported XPath expression feature is recognized.

with_traceback()

Exception.with_traceback(tb) – set self.__traceback__ to tb and return self.

Extending delb

Note

There are actually two packages that are installed with delb: delb and _delb. As the underscore indicates, the latter is exposing private parts of the API while the first is re-exposing what is deemed to be public from that one and additional contents. As a rule of thumb, use the public API in applications and the private API in delb extensions. By doing so, you can avoid circular dependencies if your extension (or other code that it depends on) uses contents from the _delb package.

delb offers a plugin system to facilitate the extendability of a few of its mechanics with Python packages. A package that extends its functionality must provide entrypoint metadata for an entrypoint group named delb that points to modules that contain extensions. Some extensions have to be decorated with specific methods of the plugin manager object. Authors are encouraged to prefix their package names with delb- in order to increase discoverability.

These extension types are currently available:

• document loaders

• document mixin classes

• document subclasses

• XPath functions

Loaders are functions that try to make sense of any given input value, and if they can they return a parsed document.

Mixin classes add functionality / attributes to the delb.Document class (instead of inheriting from it). That allows applications to rely optionally on the availability of plugins and to combine various extensions.

Subclasses can be used to provide distinct models of arbitrary aspects for contents that are represented by a specific encoding. They can optionally implement a test method to qualify them as default class for recognized contents.

The designated means of communication between extensions is the config argument to the loader respectively the instance property of a document instance with that name.

Warning

A module that contains plugins and any module it is explicitly or implicitly importing must not import anything from the delb module itself, because that would initiate the collection of plugin implementations. And these wouldn’t have been completely registered at that point. Import from the _delb module instead.

Caution

Mind to re-install a package in development when its entrypoint specification changed.

There’s a repository that outlines the mechanics as developer reference: https://github.com/delb-xml/delb-py-reference-plugins

There’s also the snakesist project that implements the loader and document mixin plugin types to interact with eXist-db as storage.

Document loaders

Loaders are registered with this decorator:

_delb.plugins.plugin_manager.register_loader(before: Optional[Union[Callable[[Any, SimpleNamespace], Union[_ElementTree, str]], Iterable[Callable[[Any, SimpleNamespace], Union[_ElementTree, str]]]]] = None, after: Optional[Union[Callable[[Any, SimpleNamespace], Union[_ElementTree, str]], Iterable[Callable[[Any, SimpleNamespace], Union[_ElementTree, str]]]]] = None) → Callable

Registers a document loader.

An example module that is specified as delb plugin for an IPFS loader might look like this:

from os import getenv
from types import SimpleNamespace
from typing import Any

from _delb.plugins import plugin_manager
from _delb.plugins.https_loader import https_loader
from _delb.typing import LoaderResult


IPFS_GATEWAY = getenv("IPFS_GATEWAY_PREFIX", "https://ipfs.io/ipfs/")


@plugin_manager.register_loader()
def ipfs_loader(source: Any, config: SimpleNamespace) -> LoaderResult:
    if isinstance(source, str) and source.startswith("ipfs://"):

        config.source_url = source
        config.ipfs_gateway_source_url = IPFS_GATEWAY + source[7:]

        return https_loader(config.ipfs_gateway_source_url, config)

    # return an indication why this loader didn't attempt to load in order
    # to support debugging
    return "The input value is not an URL with the ipfs scheme."

The source argument is what a Document instance is initialized with as input data.

Note that the config argument that is passed to a loader function contains configuration data, it’s the delb.Document.config property after _init_config has been processed.

Loaders that retrieve a document from an URL should add the origin as string to the config object as source_url.

You might want to specify a loader to be considered before or after another one. Let’s assume a loader shall figure out what to load from a remote XML resource that contains a reference to the actual document. That one would have to be considered before the one that loads XML documents from a URL with the https scheme:

from _delb.plugins import plugin_manager
from _delb.plugins.https_loader import https_loader


@plugin_manager.register_loader(before=https_loader)
def mets_loader(source, config) -> LoaderResult:
    # loading logic here
    pass

Document extensions

Document mixin classes are registered by subclassing them from this base class:

class _delb.plugins.DocumentMixinBase

By deriving a subclass from this one, a document extension class is registered as plugin. These are supposed to add additional attributes to a document, e.g. derived data or methods to interact with storage systems. All attributes of an extension should share a common prefix that terminates with an underscore, e.g. storage_load, storage_save, etc.

This base class also acts as termination for methods that can be implemented by mixin classes. Any implementation of a method must call a base class’ one, e.g.:

from types import SimpleNamespace

from _delb.plugins import DocumentMixinBase
from magic_wonderland import play_disco


class MyExtension(DocumentMixinBase):

    # this method can be implemented by any extension class
    @classmethod
    def _init_config(cls, config, kwargs):
        config.my_extension = SimpleNamespace(conf=kwargs.pop(
            "my_extension_conf"))
        super()._init_config(config, kwargs)

    # this method is specific to this extension
    def my_extension_makes_magic(self):
        play_disco()

classmethod _init_config(config: SimpleNamespace, kwargs: Dict[str, Any])

The kwargs argument contains the additional keyword arguments that a Document instance is called with. Extension classes that expect configuration data must process their specific arguments by clearing them from the kwargs dictionary, e.g. with dict.pop(), and preferably storing the final configuration data in a types.SimpleNamespace and adding it to the types.SimpleNamespace passed as config with the extension’s name. The initially mentioned keyword arguments should be prefixed with that name as well. This method is called before the loaders try to read and parse the given source for a document.

Document subclasses

Of course one can simply subclass delb.Document to add functionality. Beside using a subclass directly, you can let delb.Document figure out which subclass is an appropriate representation of the content. Subclasses can claim that by implementing a staticmethod() named _class_test__ that takes the document’s root node and the configuration to return a boolean that indicates the subclass is suited. The first class to return a True value will immediately be chosen, so be aware of the possible ambiguity in complex setups. It is only ensured that subclasses are considered before others that they derive from.

Subclasses are registered by importing them into an application, they must not be pointed to by entrypoint definitions.

Here’s an example:

class TEIDocument(Document):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **{**kwargs, "collapse_whitespace": True})

    @staticmethod
    def __class_test__(root: TagNode, config: types.SimpleNamespace) -> bool:
        return root.universal_name == "{http://www.tei-c.org/ns/1.0}TEI"

    @property
    def title(self) -> str:
        return self.css_select('titleStmt title[type="main"]').first.full_text

document = Document("""\
<?xml version="1.0" encoding="UTF-8"?>
<TEI xmlns="http://www.tei-c.org/ns/1.0"><teiHeader><fileDesc><titleStmt>
<title type="main">The Document's Title</title>
</titleStmt></fileDesc></teiHeader></TEI>
""")

if isinstance(document, TEIDocument):
    print(document.title)
else:
    print("Sorry, I don't know how to retrieve the document's title.")

The Document's Title

The recommendations as laid out for DocumentMixinHooks._init_config also apply for subclasses who would process configuration arguments in their __init__ method before calling the super class’ one.

XPath functions

Custom XPath functions are registered with this decorator:

_delb.plugins.PluginManager.register_xpath_function(self, arg: Union[Callable, str]) → Callable

Custom XPath functions can be defined as shown in the following example. The first argument to a function is always an instance of _delb.xpath.EvaluationContext followed by the expression’s arguments.

from delb import Document
from _delb.plugins import plugin_manager
from _delb.xpath import EvaluationContext


@plugin_manager.register_xpath_function("is-last")
def is_last(context: EvaluationContext) -> bool:
    return context.position == context.size

@plugin_manager.register_xpath_function
def lowercase(_, string: str) -> str:
    return string.lower()


document = Document("<root><node/><node foo='BAR'/></root>")
print(document.xpath("/*[is-last() and lowercase(@foo)='bar']").first)

<node foo="BAR"/>

Changes

Every time I thought I’d got it made

It seemed the taste was not so sweet

The listed updates resemble rather a Best Of than a full record of changes. Intentionally.

0.4 (2022-11-02)

News

• delb now uses its own XPath implementation, please investigate _delb.xpath for details.

• ⚠️Many of the nodes’ methods that relate to relative nodes have been renamed. Watch out for DeprecationWarnings!

• ⚠️The method delb.NodeBase.iterate_descendants() is added as a replacement for the former delb.NodeBase.child_nodes() invoked with the now deprecated argument recurse.

• ⚠️The https-loader extensions is now required for loading documents via plain and secured HTTP connections.

• Under the hood httpx is now employed as HTTP/S client.

• ⚠️The contributed loader for FTP connections is marked as deprecated.

• ⚠️The parser argument to delb.Document and delb.TagNode.parse() is deprecated and replaced by parser_options.

• ⚠ delb.Document.xslt() is marked as deprecated.

• ⚠️Evoked exceptions changed in various places.

• ⚠️Document mixin extensions are now facilitated by subclassing _delb.plugins.DocumentMixinBase. It replaces _delb.plugins.DocumentExtensionHooks and _delb.plugins.PluginManager.register_document_mixin() without a backward-compatible mechanic.

• Support for the very good Python 3.10 and the even better 3.11 is added.

• The code repository is now part of an umbrella namespace for related projects: https://github.com/delb-xml/

• A CITATTION.cff is available in the repository and shipped with source distributions for researchers that are citing their employed software.

0.3 (2022-01-31)

News

• Adds the delb.TagNode.fetch_or_create_by_xpath() method.

  • ⚠️Because of that a pre-mature parser of XPath expressions has been implemented and you can expect some expressions to cause failures, e.g. with functions that take more than one argument.

• Subclasses of delb.Document can claim to be the default class based on the evaluation of a document’s content and configuration by implementing __class_test__.

• ⚠️ _delb.plugins.PluginManager._register_document_extension() is renamed to _delb.plugins.PluginManager._register_document_mixin().

• ⚠️ _delb.plugins.DocumentExtensionHooks() is renamed to _delb.plugins.DocumentMixinHooks().

• ⚠️ _delb.plugins.DocumentMixinHooks._init_config() is now a classmethod() and now also takes the config namespace as first argument.

• Adds delb.Document.collapse_whitespace() and the initialization option for delb.Document instances with the same name.

• Adds the retain_child_nodes argument to delb.NodeBase.detach().

• Adds the delb.NodeBase.last_descendant property.

• Adds the delb.TagNode.id property.

• Adds the delb.TagNode.parse() method.

• ⚠️ TagNode.qualified_name() is marked deprecated and the same property is now available as TagNode.universal_name().

• Adds support for Python 3.9 & 3.10.

• ⚠️ Drops support for Python 3.6

• Uses GitHub actions for CI checks.

Fixes

• Detached delb.TagNode s now drop references to delb.TextNode siblings.

• Ensures that delb.TagNode.location_path always consists of indexed steps (/*[i]) only.

• Avoids hitting the interpreter’s recursion limit when iterating in stream dimension.

0.2 (2020-07-26)

News

• Adds a logo. Gracious thanks to sm!

• Adds plugin mechanics. Graciae ad infinitum, TC!

• CSS and XPath query results are wrapped in delb.QueryResults.

• Adds delb.Document.head_nodes and delb.Document.tail_nodes that allow access to the siblings of a root node.

• Adds the delb.Document.source_url property.

• Adds delb.get_traverser() and two traverser implementations that yield nodes related to a root node according to their defined order.

• Document loaders report back the reason why they would or could not load a document from the given object.

• Various documentation improvements, including table of contents for class members.

0.1.2 (2019-09-14)

There’s nothing super-exciting to report here. It’s just getting better.

0.1.1 (2019-08-15)

This was quiet boring, it serves updated dependencies for what it’s worth.

0.1 (2019-05-26)

The initial release with a set and sound data model and API.

Glossary

filter

Filter functions can be used as arguments with various methods on node instances that return other nodes. They are called with a node instance as only argument and they should return a bool to indicate whether the node matches the filter. Have a look at the Filters source code for examples.

tag node

Tag nodes are the equivalent to the DOM’s element node. Its name shall make it distinguishable from the ElementTree API and relates to the nodes’ functionality of tagging text.

Index

License

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not convey it at all.  For example, if you agree to terms that obligate you
to collect a royalty for further conveying from those to whom you convey
the Program, the only way you could satisfy both those terms and this
License would be to refrain entirely from conveying the Program.

  13. Remote Network Interaction; Use with the GNU General Public License.

  Notwithstanding any other provision of this License, if you modify the
Program, your modified version must prominently offer all users
interacting with it remotely through a computer network (if your version
supports such interaction) an opportunity to receive the Corresponding
Source of your version by providing access to the Corresponding Source
from a network server at no charge, through some standard or customary
means of facilitating copying of software.  This Corresponding Source
shall include the Corresponding Source for any work covered by version 3
of the GNU General Public License that is incorporated pursuant to the
following paragraph.

  Notwithstanding any other provision of this License, you have
permission to link or combine any covered work with a work licensed
under version 3 of the GNU General Public License into a single
combined work, and to convey the resulting work.  The terms of this
License will continue to apply to the part which is the covered work,
but the work with which it is combined will remain governed by version
3 of the GNU General Public License.

  14. Revised Versions of this License.

  The Free Software Foundation may publish revised and/or new versions of
the GNU Affero General Public License from time to time.  Such new versions
will be similar in spirit to the present version, but may differ in detail to
address new problems or concerns.

  Each version is given a distinguishing version number.  If the
Program specifies that a certain numbered version of the GNU Affero General
Public License "or any later version" applies to it, you have the
option of following the terms and conditions either of that numbered
version or of any later version published by the Free Software
Foundation.  If the Program does not specify a version number of the
GNU Affero General Public License, you may choose any version ever published
by the Free Software Foundation.

  If the Program specifies that a proxy can decide which future
versions of the GNU Affero General Public License can be used, that proxy's
public statement of acceptance of a version permanently authorizes you
to choose that version for the Program.

  Later license versions may give you additional or different
permissions.  However, no additional obligations are imposed on any
author or copyright holder as a result of your choosing to follow a
later version.

  15. Disclaimer of Warranty.

  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

  16. Limitation of Liability.

  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
SUCH DAMAGES.

  17. Interpretation of Sections 15 and 16.

  If the disclaimer of warranty and limitation of liability provided
above cannot be given local legal effect according to their terms,
reviewing courts shall apply local law that most closely approximates
an absolute waiver of all civil liability in connection with the
Program, unless a warranty or assumption of liability accompanies a
copy of the Program in return for a fee.