PyParsing -- A Python Parsing Module

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Introduction

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The pyparsing module is an alternative approach to creating and

executing simple grammars, vs. the traditional lex/yacc approach, or the

use of regular expressions. The pyparsing module provides a library of

classes that client code uses to construct the grammar directly in

Python code.

*[Since first writing this description of pyparsing in late 2003, this

technique for developing parsers has become more widespread, under the

name Parsing Expression Grammars - PEGs. See more information on PEGs at*

https://en.wikipedia.org/wiki/Parsing_expression_grammar *.]*

Here is a program to parse ``"Hello, World!"`` (or any greeting of the form

``"salutation, addressee!"``):

.. code:: python

from pyparsing import Word, alphas

greet = Word(alphas) + "," + Word(alphas) + "!"

hello = "Hello, World!"

print(hello, "->", greet.parseString(hello))

The program outputs the following::

Hello, World! -> ['Hello', ',', 'World', '!']

The Python representation of the grammar is quite readable, owing to the

self-explanatory class names, and the use of '+', '|' and '^' operator

definitions.

The parsed results returned from ``parseString()`` can be accessed as a

nested list, a dictionary, or an object with named attributes.

The pyparsing module handles some of the problems that are typically

vexing when writing text parsers:

- extra or missing whitespace (the above program will also handle ``"Hello,World!"``, ``"Hello , World !"``, etc.)

- quoted strings

- embedded comments

The examples directory includes a simple SQL parser, simple CORBA IDL

parser, a config file parser, a chemical formula parser, and a four-

function algebraic notation parser, among many others.

Documentation

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There are many examples in the online docstrings of the classes

and methods in pyparsing. You can find them compiled into online docs

at https://pyparsing-docs.readthedocs.io/en/latest/. Additional

documentation resources and project info are listed in the online

GitHub wiki, at https://github.com/pyparsing/pyparsing/wiki. An

entire directory of examples is at

https://github.com/pyparsing/pyparsing/tree/master/examples.

License

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MIT License. See header of pyparsing.py

History

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See CHANGES file.

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