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Python bindings for bison/flex parser engine

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Welcome to PyBison!
Bringing GNU Bison/Flex's raw speed and power to Python

What is PyBison?

PyBison is a framework which effectively 'wraps' Bison and Flex into a Python class structure.

You define a parser class, define tokens and precedences as attributes, and parse targets as methods with rules in the docstrings, then instantiate and run.

Black Magick happens in the background, whereupon you get callbacks each time yyparse() resolves a parse target.


Now, install pybison with:

pip install pybison

The following command will verify if the installation succeeded:

python -c "import bison"

There are already parsers for Python. Why re-invent the wheel?

I looked at all the Python-based parsing frameworks.

IMO, the best one was PLY - a pure-python lexx/yacc implementation (which I have borrowed from heavily in designing PyBison's OO model).

But PLY suffers some major limitations:

  • usage of 'named groups' regular expressions in the lexer creates a hard limit of 100 tokens - not enough to comfortably handle major languages
  • pure-python implementation is a convenience, but incurs a cruel performance penalty
  • the parser engine is SLR, not full LALR(1)

The other frameworks utilise a fiddly script syntax -

How do I use this?

Refer to the examples and the docs for usage.


You will need:

We assume that Python, pip and a C compiler is already installed.


First, install the dependencies bison and flex.

Arch Linux

sudo pacman -S bison flex


sudo apt-get install bison flex


With Chocolatey, you can install the packages as follows:

choco install winflexbison3

Additionally, if a C compiler is needed, mingw can be installed with Chocolatey as well.

choco install mingw


See the short introduction into debugging.


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