PyParsing -- A Python Parsing Module

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Introduction

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

__ .]

Here is a program to parse

(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

is a collection of type

ParseResults

, which 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

There are many examples in the online docstrings of the classes and methods in pyparsing. You can find them compiled into

. Additional documentation resources and project info are listed in the online

GitHub wiki <https://github.com/pyparsing/pyparsing/wiki>

. An entire directory of examples can be found

here <https://github.com/pyparsing/pyparsing/tree/master/examples>

__.

License

MIT License. See header of the

__ file.

History

See

__ file.

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