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The Omega parsing framework

Project Description


Omega is a framework designed to help you build parsers for text and binary data. It creates a recursive-descent/Parsing-Expression-Grammar parser given a description of the file-format in the concise Omega language, but if your file-format can’t be described in pure Omega, it’s easy to extend with Python.

For example, here’s a very simple parser for arithmetic expressions:

>>> import omega
>>> class ArithmeticParser(omega.BaseParser):
...     __grammar = """
...             digit = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7'
...                     | '8' | '9' ;
...             term = digit+:ds -> (int("".join(ds)))
...                     | '(' sum:s ')' -> (s)
...                     ;
...             product = term:a '*' product:b -> (a * b)
...                     | term:a '/' product:b -> (a / b)
...                     | term
...                     ;
...             sum = product:a '+' sum:b -> (a + b)
...                     | product:a '-' sum:b -> (a - b)
...                     | product
...                     ;
...         """

And here it is in action:

>>> ArithmeticParser.match("1")
>>> ArithmeticParser.match("1+1")
>>> ArithmeticParser.match("6*9")
>>> ArithmeticParser.match("2+3*4")
>>> ArithmeticParser.match("(2+3)*4")

Omega is heavily based on ideas from Alessandro Warth’s [OMeta package][1] for Smalltalk and JavaScript, but translated to fit as naturally as possible into Python.



Omega is a pure-Python package, and requires only Python 3.4 or higher to be installed.

What’s In The Box

  • is this file.
  • is a list of possible future additions to the package.
  • LICENCE is the full text of the licence this software is released under, the GPLv3.
  • is the standard Python packaging script.
  • docs is a subdirectory containing all the documentation for Omega, including language and library references, a Python API reference, and a tutorial.
  • examples is a subdirectory containing various self-contained example parsers written in Omega.
  • omega is the Python package itself.


Omega uses the standard distutils packaging system for Python, so if you have a source tarball, you should be able to install it with:

python install

…and of course all the other standard distutils commands are available.


The complete documentation is packaged with Omega source releases, and is also available online at

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