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The pyparsing module is an alternative approach to creating andexecuting simple grammars, vs. the traditional lex/yacc approach, or theuse of regular expressions. The pyparsing module provides a library ofclasses that client code uses to construct the grammar directly inPython code.

[Since first writing this description of pyparsing in late 2003, thistechnique for developing parsers has become more widespread, under thename Parsing Expression Grammars - PEGs. See more information on PEGshere.]

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

frompyparsingimportWord,alphasgreet=Word(alphas)+","+Word(alphas)+"!"hello="Hello, World!"print(hello,"->",greet.parse_string(hello))

The program outputs the following:

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

The Python representation of the grammar is quite readable, owing to theself-explanatory class names, and the use of '+', '|' and '^' operatordefinitions.

The parsed results returned fromparse_string() is a collection of typeParseResults, which can be accessed as anested list, a dictionary, or an object with named attributes.

The pyparsing module handles some of the problems that are typicallyvexing 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 IDLparser, a config file parser, a chemical formula parser, and a four-function algebraic notation parser, among many others.

There are many examples in the online docstrings of the classesand methods in pyparsing. You can find them compiled intoonline docs. Additionaldocumentation resources and project info are listed in the onlineGitHub wiki. Anentire directory of examples can be foundhere.

MIT License. See header of thepyparsing __init__.py file.

SeeCHANGES file.