https://github.com/moreati/ppeg
A Python port of Lua's LPeg pattern matching library
https://github.com/moreati/ppeg
Last synced: about 1 month ago
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A Python port of Lua's LPeg pattern matching library
- Host: GitHub
- URL: https://github.com/moreati/ppeg
- Owner: moreati
- License: mit
- Created: 2015-10-22T14:35:43.000Z (almost 10 years ago)
- Default Branch: master
- Last Pushed: 2015-11-17T18:59:02.000Z (almost 10 years ago)
- Last Synced: 2025-08-25T08:31:18.825Z (about 2 months ago)
- Language: C
- Homepage:
- Size: 347 KB
- Stars: 7
- Watchers: 4
- Forks: 2
- Open Issues: 13
-
Metadata Files:
- Readme: README.rst
- Changelog: CHANGELOG.rst
- License: LICENSE
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README
====
PPeg
====
*PPeg* is a pattern matching library for Python, based on
`Parsing Expression Grammars`_ (PEGs).
It's a port of the `LPeg`_ library from Lua.
.. warning::
PPeg is alpha software, it's not ready for general use.
There are bugs, and they will crash/coredeump your Python process.
.. warning::
PPeg is experimental. The API and semantics are not stable.
Future releases will break backward compatibility, without warning.
.. _Parsing Expression Grammars: https://en.wikipedia.org/wiki/Parsing_expression_grammar
.. _LPeg: http://www.inf.puc-rio.br/~roberto/lpeg/
Usage
=====
Unlike the ``re`` module [#]_, PPeg patterns can handle balanced sequences
.. code:: python
>>> from _ppeg import Pattern as P
>>> pattern = P.Grammar('(' + ( (P(1)-P.Set('()')) | P.Var(0) )**0 + ')')
>>> pattern('(foo(bar()baz))').pos
15
>>> pattern('(foo(bar(baz)').pos
-1
>>> capture = P.Cap(pattern)
>>> capture('(foo(bar()baz))').captures
['(foo(bar()baz))']
This example corresponds roughly to the following LPeg example
.. code:: lua
> lpeg = require "lpeg"
> pattern = lpeg.P{ "(" * ((1 - lpeg.S"()") + lpeg.V(1))^0 * ")" }
> pattern:match("(foo(bar()baz))") -- Lua indexes begin at 1
16
> pattern:match("(foo(bar(baz)")
nil
> capture = lpeg.C(pattern)
> capture:match("(foo(bar()baz))")
"(foo(bar()baz))"
.. [#] Some regular expression implementations (e.g. PCRE_, regex_)
support `recursive patterns`_, which can match balanced sequences.
.. _pcre: http://www.pcre.org/
.. _regex: https://pypi.python.org/pypi/regex
.. _recursive patterns: http://www.regular-expressions.info/recurse.html
Limitations
===========
- PPeg only supports CPython 2.6 and 2.7.
- PPeg doesn't support Unicode, only byte strings can be matched or searched.
This is closely tied to how Lua and LPeg handle strings.
- PPeg is untested on any platform except 64-bit Linux.
- Bugs, lots of bugs.