XPath 1.0/2.0 parsers and selectors for ElementTree.
Project description
The proposal of this package is to provide XPath 1.0 and 2.0 selectors for Python’s ElementTree XML data structures, both for the standard ElementTree library and for the lxml.etree library.
For lxml.etree this package could be useful for providing XPath 2.0 selectors, because lxml.etree already has it’s own implementation of XPath 1.0.
The XPath 2.0 functions implementation is partial, due to wide number of functions that this language provides. If you want you can contribute to add an unimplemented function see the section below.
Installation and usage
You can install the package with pip in a Python 2.7 or Python 3.3+ environment:
pip install elementpath
For using import the package and apply the selectors on ElementTree nodes:
>>> import elementpath
>>> from xml.etree import ElementTree
>>> xt = ElementTree.XML('<A><B1/><B2><C1/><C2/><C3/></B2></A>')
>>> elementpath.select(xt, '/A/B2/*')
...Public API
The package includes some classes and functions for XPath parsers and selectors.
XPath1Parser
class XPath1Parser(namespaces=None, variables=None, strict=True)The XPath 1.0 parser. Provide a namespaces dictionary argument for mapping namespace prefixes to URI inside expressions. With variables you can pass a dictionary with the static context’s in-scope variables. If strict is set to False the parser enables parsing of QNames, like the ElementPath library.
XPath2Parser
XPath2Parser(namespaces=None, variables=None, strict=True, default_namespace='', function_namespace=None,
schema=None, build_constructors=False, compatibility_mode=False)The XPath 2.0 parser, that is the default parser. It has additional arguments compared to the parent class. default_namespace is the namespace to apply to unprefixed names. For default no namespace is applied (the empty namespace ‘’). function_namespace is the default namespace to apply to unprefixed function names (the “http://www.w3.org/2005/xpath-functions” namespace for default). schema is an optional instance of an XML Schema interface as defined by the abstract class AbstractSchemaProxy. build_constructors indicates when to define constructor functions for the in-scope XSD atomic types. The compatibility_mode flag indicates if the XPath 2.0 parser has to work in compatibility with XPath 1.0.
XPath selectors
select(root, path, namespaces=None, schema=None, parser=XPath2Parser)Apply path expression on root Element. The root argument can be an ElementTree instance or an Element instance. Returns a list with XPath nodes or a basic type for expressions based on a function or literal.
iter_select(root, path, namespaces=None, schema=None, parser=XPath2Parser)Iterator version of select, if you want to process each result one by one.
Selector(path, namespaces=None, schema=None, parser=XPath2Parser)Create an instance of this class if you want to apply an XPath selector to several target data. An instance provides select and iter_select methods with a root argument that has the same meaning that as for the select API.
Contributing
You can contribute to this package reporting bugs, using the issue tracker or by a pull request. In case you open an issue please try to provide a test or test data for reproducing the wrong behaviour. The provided testing code shall be added to the tests of the package.
The XPath parsers are based on an implementation of the Pratt’s Top Down Operator Precedence parser. The implemented parser includes some lookup-ahead features, helpers for registering tokens and for extending language implementations. Also the token class has been generalized using a MutableSequence as base class. See tdop_parser.py for the basic internal classes and xpath1_parser.py for extensions and for a basic usage of the parser.
If you like you can use the basic parser and tokens provided by the tdop_parser.py module to implement other types of parsers (I think it could be also a funny exercise!).
License
This software is distributed under the terms of the MIT License. See the file ‘LICENSE’ in the root directory of the present distribution, or http://opensource.org/licenses/MIT.
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