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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 <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()`` 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 `online docs <https://pyparsing-docs.readthedocs.io/en/latest/>`__. 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 `pyparsing.py <https://github.com/pyparsing/pyparsing/blob/master/pyparsing/__init__.py#L1-L23>`__ file.
History
=======
See `CHANGES <https://github.com/pyparsing/pyparsing/blob/master/CHANGES>`__ file.
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