77 lines
2.4 KiB
ReStructuredText
77 lines
2.4 KiB
ReStructuredText
PyParsing -- A Python Parsing Module
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====================================
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|Build Status|
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Introduction
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============
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The pyparsing module is an alternative approach to creating and
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executing simple grammars, vs. the traditional lex/yacc approach, or the
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use of regular expressions. The pyparsing module provides a library of
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classes that client code uses to construct the grammar directly in
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Python code.
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*[Since first writing this description of pyparsing in late 2003, this
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technique for developing parsers has become more widespread, under the
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name Parsing Expression Grammars - PEGs. See more information on PEGs at*
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https://en.wikipedia.org/wiki/Parsing_expression_grammar *.]*
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Here is a program to parse ``"Hello, World!"`` (or any greeting of the form
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``"salutation, addressee!"``):
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.. code:: python
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from pyparsing import Word, alphas
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greet = Word(alphas) + "," + Word(alphas) + "!"
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hello = "Hello, World!"
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print(hello, "->", greet.parseString(hello))
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The program outputs the following::
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Hello, World! -> ['Hello', ',', 'World', '!']
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The Python representation of the grammar is quite readable, owing to the
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self-explanatory class names, and the use of '+', '|' and '^' operator
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definitions.
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The parsed results returned from ``parseString()`` can be accessed as a
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nested list, a dictionary, or an object with named attributes.
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The pyparsing module handles some of the problems that are typically
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vexing when writing text parsers:
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- extra or missing whitespace (the above program will also handle ``"Hello,World!"``, ``"Hello , World !"``, etc.)
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- quoted strings
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- embedded comments
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The examples directory includes a simple SQL parser, simple CORBA IDL
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parser, a config file parser, a chemical formula parser, and a four-
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function algebraic notation parser, among many others.
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Documentation
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=============
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There are many examples in the online docstrings of the classes
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and methods in pyparsing. You can find them compiled into online docs
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at https://pyparsing-docs.readthedocs.io/en/latest/. Additional
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documentation resources and project info are listed in the online
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GitHub wiki, at https://github.com/pyparsing/pyparsing/wiki. An
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entire directory of examples is at
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https://github.com/pyparsing/pyparsing/tree/master/examples.
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License
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=======
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MIT License. See header of pyparsing.py
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History
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=======
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See CHANGES file.
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.. |Build Status| image:: https://travis-ci.org/pyparsing/pyparsing.svg?branch=master
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:target: https://travis-ci.org/pyparsing/pyparsing
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