Parse XPATH 3.1 using Pyparsing

XPath (XML Path Language) is a query language for selecting nodes from an XML document. In addition, XPath is used to compute values (e.g., strings, numbers, or Boolean values) from the content of an XML document. XPath is maintained by the World Wide Web Consortium (W3C).

Pyparsing is a parsing module used to construct grammar in Python. XPyth-parser uses Pyparsing to parse XPath strings, and offers an additional abstraction layer.

Status

This library is an attempt to create a parser which can be used both to query XML documents, as well as calculation tasks. The original plan was to support both options. However, XPath 3.1 is not widely used, so use cases are sparse. Parsing XPath 3.1 on a grammar level should still be supported, but not all information may be available when using the abstraction layer. Most importantly, there will be XPath functions missing.

Dealing with dynamic contexts (i.e., parsing XML as Parser.xml will be done using LXML for now). In a way, XPyth-parser is at the present moment a fancy wrapper around LXML, in order to support some XPath 2.0+ functionality.

Alternatives

For most use cases, there will be (better) alternatives to this project. LXML is Pythonic binding for the C libraries libxml2 and libxslt. If only XPath 1.0 is needed, LXML will be a better solution.

Requirements

xpyth-parser depends on LXML, PyParsing. For parsing dates we use Isodate.

Goals

This project started out with a specific goal: to parse XBRL formula tests. These tests are heavily reliant on XBRL specific XPath 2.0 functions. Because of this, the author of this library is focussing on correctly interpreting these functions.

Examples

from xpyth_parser.parse import Parser 
count = Parser("count(1,2,3)").run()
print(count) -> 3

This will give a wrapper class which contains the resolved syntax tree in count.XPath and the answer in count.resolved_answer

Parsing only

It is also possible to only parse the string, but not try to resolve the static and dynamic context

count = Parser("count(1,2,3), no_resolve=True")

count.xpath will be the full syntax tree, instead of having functions processed and contexts applied. count.run() will resolve the expression as if no_resolve=False. contexts might need to be passed to the object beforehand.