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I need to parse (not to evaluate) Xpath expressions in Python to change them, e.g. I have expressions like 

//div[...whatever...]//some-other-node...

and I need to change them to (for example):

/changed-node[@attr='value' and ...whatever...]/another-changed-node[@attr='value' ...

As it seems to me I need to split the original expression to steps and the steps to axes+nodes and predicates. Is there some tool I can do it with or is there a nice and easy way to do it without one?

The catch is I can't be sure that the predicates of original expressions won't contain something like [@id='some/value/with/slashes'] so I can't parse them with naive regexes.

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You might be able to use the REx parser generator from Gunther Rademacher. See http://www.bottlecaps.de/rex/ This will generate a parser for any grammar from a suitable BNF, and suitable BNF for various XPath versions is available. REx is a superb piece of technology spoilt only by extremely poor documentation. It can generate parsers in a number of languages including Javascript, XQuery, and XSLT. It's used in the Saxon-JS product to parse dynamic XPath expressions within the browser.

Another approach is to use the XQuery to XQueryX converters available from W3C (XPath is a subset of XQuery so these will handle XPath as well. These produce a representation of the syntax tree in XML).

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2024 Update: Rex is now (finally!) available as open source at github.com/GuntherRademacher/rex-parser-generator

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