Pyparsing pdf

For brevity, fn may also be a lambda - here is an example of using a parse action to convert matched integer tokens from strings to integers:. If fn modifies the toks list in-place, it does not need to return and pyparsing will use the modified toks list. Takes a method that takes the same arguments, but simply returns True or False.

If False is returned, an exception will be raised. To define an identifier using a Word , use either of the following:. Pyparsing also provides pre-defined strings identchars and identbodychars so that you can also write:. If only one string given, it specifies that the same character set defined for the initial character is used for the word body; for instance, to define an identifier that can only be composed of capital letters and underscores, use one of:.

A Word may also be constructed with any of the following optional parameters:. If exact is specified, it will override any values for min or max. Previously, you would have to create a custom string to pass to Word. Char - a convenience form of Word that will match just a single character from a string of matching characters:. CharsNotIn - similar to Word , but matches characters not in the given constructor string accepts only one string for both initial and body characters ; also supports min , max , and exact optional parameters.

Regex - a powerful construct, that accepts a regular expression to be matched at the current parse position; accepts an optional flags parameter, corresponding to the flags parameter in the re. QuotedString allows you to specify the following parameters:. SkipTo - skips ahead in the input string, accepting any characters up to the specified pattern; may be constructed with the following optional parameters:. SkipTo can also be written using Opt - construct with a ParserElement , but this element is not required to match; can be constructed with an optional default argument, containing a default string or object to be supplied if the given optional parse element is not found in the input string; parse action will only be called if a match is found, or if a default is specified.

Opt was formerly named Optional , but since the standard Python library module typing now defines Optional , the pyparsing class has been renamed to Opt. A compatibility synonym Optional is defined, but will be removed in a future release. FollowedBy - a lookahead expression, requires matching of the given expressions, but does not advance the parsing position within the input string.

ParseResults - class used to contain and manage the lists of tokens created from parsing the input using the user-defined parse expression. ParseResults can be accessed in a number of ways:.

Note that this will strip the results of any field names that have been defined for any embedded parse elements. Finally, ParseResults can be viewed by calling dump. ParseException - exception returned when a grammar parse fails; ParseExceptions have attributes loc , msg , line , lineno , and column ; to view the text line and location where the reported ParseException occurs, use:.

ParseExceptions also have an explain method that gives this same information:. RecursiveGrammarException - exception returned by validate if the grammar contains a recursive infinite loop, such as:.

ParseFatalException - exception that parse actions can raise to stop parsing immediately. Should be used when a semantic error is found in the input text, such as a mismatched XML tag.

Diagnostics can be enabled using pyparsing. All warnings can be enabled by calling pyparsing. If using -Wd for testing, but wishing to disable pyparsing warnings, add -Wipyparsing. By default, the delimiters are suppressed, so the returned results contain only the separate list elements.

Returns an expression that parses the leading integer, reads exactly that many expressions, and returns the array of expressions in the parse results - the leading integer is suppressed from the results although it is easily reconstructed by using len on the returned array. The values are sorted so that longer matches are attempted first; this ensures that a short value does not mask a longer one that starts with the same characters. For instance:. If an expression is not provided for the content argument, the nested expression will capture all whitespace-delimited content between delimiters as a list of separate values.

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The pyparsing module is an alternative approach to creating and executing simple grammars, vs. The pyparsing module provides a library of classes that client code uses to construct the grammar directly in Python code.

See more information on PEGs here. Here is a program to parse "Hello, World! 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:.

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. MIT License. See header of the pyparsing. Nov 12, Nov 7, Oct 30, Oct 27, Oct 24, Oct 23, Oct 2, Sep 9, Aug 8, Dec 30, Nov 3, Jun 28, Apr 5, Dec 25, Nov 10, Nov 5,