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pyre2 Documentation

repository·main·Indexed 20 days ago

https://github.com/facebook/pyre2

A Python wrapper for Google's RE2 regular expression library providing a compatible interface to the built-in re module. It offers linear time complexity guarantees and specialized methods like test_search, test_match, and test_fullmatch for performance-sensitive tasks, though it lacks support for substitution, flags, and certain iteration methods.

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What's inside pyre2

  1. What is pyre2?

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    pyre2 is a Python extension that wraps Google's RE2 regular expression library. It provides a Python interface that implements many features of the built-in re module, making it a drop-in replacement for performance-sensitive regex tasks where RE2's guarantees (like linear time complexity) are required.

  2. Use pyre2 Regexp methods

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    pyre2 provides Regexp objects with several methods for matching.

    Key features include:

    • fullmatch: Works like match, but anchors the match at both the start and the end of the string.
    • test_search, test_match, and test_fullmatch: These methods return a boolean (True or False) indicating if a match was successful. They are generally faster than the standard search/match/fullmatch methods, particularly when using patterns with capturing groups, because they avoid the overhead of constructing match objects.

  3. Understand the limitations of pyre2

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    pyre2 is a subset of the standard re module. When using it, be aware of the following missing features:

    • No substitution methods: You cannot perform string replacements.
    • No flags: Regex flags (like re.IGNORECASE) are not supported.
    • No iteration/splitting: split, findall, and finditer are not implemented.
    • No top-level convenience functions: You cannot call pyre2.search() or pyre2.match() directly. You must first use compile() to create a Regexp object.
    • No compile cache: Performance-critical applications should manage their own pattern caching.
    • Match object limitations: Match objects do not support lastindex or lastgroup.

  4. Build pyre2 with RE2

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    Because RE2 does not build with fPIC by default, you must include specific CFLAGS when building the RE2 library itself:

    make CFLAGS='-fPIC -c -Wall -Wno-sign-compare -O3 -g -I.'

    When building the pyre2 Python module, you must provide the include and library paths for RE2 using CPPFLAGS and LDFLAGS:

    env CPPFLAGS='-I/path/to/re2' LDFLAGS='-L/path/to/re2/obj' ./setup.py build
    make CFLAGS='-fPIC -c -Wall -Wno-sign-compare -O3 -g -I.'

env CPPFLAGS='-I/path/to/re2' LDFLAGS='-L/path/to/re2/obj' ./setup.py build