==== 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.