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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.
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.
License
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MIT License. See header of pyparsing.py
History
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See CHANGES file.
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