pyparsing / plusminus

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.

[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 .]

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() 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. Additional documentation resources and project info are listed in the online GitHub wiki. An entire directory of examples can be found here.

License

MIT License. See header of the pyparsing __init__.py file.

History

See CHANGES file.

plusminus's Issues

Support for decimal.Decimal and other numerical types as an alternative to float

I'd like there be an option like parser = BaseArithmeticParser(numerical_types=[int, Decimal, complex]) where if numerical_types=None it would default to the value numerical_types=[int, float, complex] so that when I'm dealing with monetary values I can be confident that the answer IS EXACT, not really super close.

Refactor parsers to separate Python eval() features from standard Arithmetic features

plusminus is a project of 2 minds:

• being a safe alternative to Python eval()
• implementing common arithmetic notations and operations, often using Unicode operators or notation that are not supported in Python (such as |x| for abs(x))

These two goals should be split into separate parser classes, so that "programming-ish" concepts do not necessarily bleed over into arithmetic notations, and arithmetic expressions like |x| are not included in safe Python eval() support.

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More variances in variable names

Hi,

Thanks for your great work on pyparsing and plusminus.

I am searching for a parser working on pandas Series with variables.
This looks to work out of the box with plusminus (mapping all series of a dataframe to variables)
For a 1:1 adaption it would be fine to have a different identifier definition.

As the data columns i am working (they come from external CSV) on may contain spaces i would like to define a variable as

var_name = pp.QuotedString('[', endQuoteChar=']').setName("identifier")

which currently requires a copy and paste of your library.

Christoph