PyParsing -- A Python Parsing Module

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.

Here is a program to parse "Hello, World!" (or any greeting of the form "salutation, addressee!"):

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 .zip file includes examples of a simple SQL parser, simple CORBA IDL parser, a config file parser, a chemical formula parser, and a four- function algebraic notation parser. It also includes a simple how-to document, and a UML class diagram of the library's classes.

Installation

Do the usual:

python setup.py install

(pyparsing requires Python 2.6 or later.)

Or corresponding commands using pip, easy_install, or wheel:

pip install pyparsing

easy_install pyparsing

wheel install pyparsing

Documentation

See:

HowToUsePyparsing.html

License

MIT License. See header of pyparsing.py

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