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pyparsing module - Classes and methods to define and execute parsing grammars
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. With pyparsing, you don't need to learn a new syntax for defining grammars or matching expressions - the parsing module provides a library of classes that you use to construct the grammar directly in Python.
Here is a program to parse "Hello, World!" (or any greeting
of the form "<salutation>,
<addressee>!"
):
from pyparsing import Word, alphas # define grammar of a greeting 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 '^' operators.
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:
Version: 1.5.5
Author: Paul McGuire <ptmcg@users.sourceforge.net>
Classes | |
ParseBaseException base exception class for all parsing runtime exceptions |
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ParseException exception thrown when parse expressions don't match class; supported attributes by name are: |
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ParseFatalException user-throwable exception thrown when inconsistent parse content is found; stops all parsing immediately |
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ParseSyntaxException just like ParseFatalException , but thrown internally
when an ErrorStop ('-' operator) indicates that
parsing is to stop immediately because an unbacktrackable syntax
error has been found
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RecursiveGrammarException exception thrown by validate() if the grammar could be
improperly recursive
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ParseResults Structured parse results, to provide multiple means of access to the parsed data: |
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ParserElement Abstract base level parser element class. |
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Token Abstract ParserElement subclass, for defining atomic
matching patterns.
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Empty An empty token, will always match. |
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NoMatch A token that will never match. |
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Literal Token to exactly match a specified string. |
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Keyword Token to exactly match a specified string as a keyword, that is, it must be immediately followed by a non-keyword character. |
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CaselessLiteral Token to match a specified string, ignoring case of letters. |
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CaselessKeyword | |
Word Token for matching words composed of allowed character sets. |
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Regex Token for matching strings that match a given regular expression. |
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QuotedString Token for matching strings that are delimited by quoting characters. |
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CharsNotIn Token for matching words composed of characters *not* in a given set. |
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White Special matching class for matching whitespace. |
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GoToColumn Token to advance to a specific column of input text; useful for tabular report scraping. |
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LineStart Matches if current position is at the beginning of a line within the parse string |
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LineEnd Matches if current position is at the end of a line within the parse string |
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StringStart Matches if current position is at the beginning of the parse string |
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StringEnd Matches if current position is at the end of the parse string |
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WordStart Matches if the current position is at the beginning of a Word, and is not preceded by any character in a given set of wordChars (default= printables ).
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WordEnd Matches if the current position is at the end of a Word, and is not followed by any character in a given set of wordChars (default= printables ).
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ParseExpression Abstract subclass of ParserElement, for combining and post-processing parsed tokens. |
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And Requires all given ParseExpressions to be found in the
given order.
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Or Requires that at least one ParseExpression is found.
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MatchFirst Requires that at least one ParseExpression is found.
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Each Requires all given ParseExpressions to be found, but
in any order.
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ParseElementEnhance Abstract subclass of ParserElement , for combining and
post-processing parsed tokens.
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FollowedBy Lookahead matching of the given parse expression. |
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NotAny Lookahead to disallow matching with the given parse expression. |
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ZeroOrMore Optional repetition of zero or more of the given expression. |
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OneOrMore Repetition of one or more of the given expression. |
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Optional Optional matching of the given expression. |
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SkipTo Token for skipping over all undefined text until the matched expression is found. |
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Forward Forward declaration of an expression to be defined later - used for recursive grammars, such as algebraic infix notation. |
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TokenConverter Abstract subclass of ParseExpression, for converting parsed results. |
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Upcase Converter to upper case all matching tokens. |
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Combine Converter to concatenate all matching tokens to a single string. |
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Group Converter to return the matched tokens as a list - useful for returning tokens of ZeroOrMore and OneOrMore expressions. |
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Dict Converter to return a repetitive expression as a list, but also as a dictionary. |
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Suppress Converter for ignoring the results of a parsed expression. |
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OnlyOnce Wrapper for parse actions, to ensure they are only called once. |
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Variables | |
alphas =
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nums =
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hexnums =
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alphanums =
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printables =
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empty = empty
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lineStart = lineStart
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lineEnd = lineEnd
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stringStart = stringStart
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stringEnd = stringEnd
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opAssoc = _Constants()
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dblQuotedString = string enclosed in double quotes
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sglQuotedString = string enclosed in single quotes
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quotedString = quotedString using single or double quotes
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unicodeString = Combine:({"u" quotedString using single or dou
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alphas8bit =
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punc8bit =
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commonHTMLEntity = Combine:({"&" Re:('gt|lt|amp|nbsp|quot') ";"})
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cStyleComment = C style comment
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htmlComment = Re:('<!--[\\s\\S]*?-->')
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restOfLine = Re:('.*')
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dblSlashComment = // comment
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cppStyleComment = C++ style comment
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javaStyleComment = C++ style comment
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pythonStyleComment = Python style comment
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commaSeparatedList = commaSeparatedList
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anyCloseTag = </W:(abcd...,abcd...)>
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anyOpenTag = <W:(abcd...,abcd...)>
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Function Details |
Returns current column within a string, counting newlines as line separators. The first column is number 1. Note: the default parsing behavior is to expand tabs in the input string before starting the parsing process. See ParserElement.parseString for more information on parsing strings containing <TAB>s, and suggested methods to maintain a consistent view of the parsed string, the parse location, and line and column positions within the parsed string. |
Returns current line number within a string, counting newlines as line separators. The first line is number 1. Note: the default parsing behavior is to expand tabs in the input string before starting the parsing process. See ParserElement.parseString for more information on parsing strings containing <TAB>s, and suggested methods to maintain a consistent view of the parsed string, the parse location, and line and column positions within the parsed string. |
Helper to define a delimited list of expressions - the delimiter
defaults to ','. By default, the list elements and delimiters can have
intervening whitespace, and comments, but this can be overridden by
passing |
Helper to define a counted list of expressions. This helper defines a pattern of the form: integer expr expr expr... where the leading integer tells how many expr expressions follow. The matched tokens returns the array of expr tokens as a list - the leading count token is suppressed. |
Helper to define an expression that is indirectly defined from the tokens matched in a previous expression, that is, it looks for a 'repeat' of a previous expression. For example: first = Word(nums) second = matchPreviousLiteral(first) matchExpr = first + ":" + second will match |
Helper to define an expression that is indirectly defined from the tokens matched in a previous expression, that is, it looks for a 'repeat' of a previous expression. For example: first = Word(nums) second = matchPreviousExpr(first) matchExpr = first + ":" + second will match |
Helper to quickly define a set of alternative Literals, and makes sure
to do longest-first testing when there is a conflict, regardless of the
input order, but returns a Parameters:
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Helper to easily and clearly define a dictionary by specifying the
respective patterns for the key and value. Takes care of defining the
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Helper to return the original, untokenized text for a given
expression. Useful to restore the parsed fields of an HTML start tag
into the raw tag text itself, or to revert separate tokens with
intervening whitespace back to the original matching input text. Simpler
to use than the parse action If the optional |
Helper to easily define string ranges for use in Word construction. Borrows syntax from regexp '[]' string range definitions: srange("[0-9]") -> "0123456789" srange("[a-z]") -> "abcdefghijklmnopqrstuvwxyz" srange("[a-z$_]") -> "abcdefghijklmnopqrstuvwxyz$_" The input string must be enclosed in []'s, and the returned string is the expanded character set joined into a single string. The values enclosed in the []'s may be: a single character an escaped character with a leading backslash (such as \- or \]) an escaped hex character with a leading '\0x' (\0x21, which is a '!' character) an escaped octal character with a leading '\0' (\041, which is a '!' character) a range of any of the above, separated by a dash ('a-z', etc.) any combination of the above ('aeiouy', 'a-zA-Z0-9_$', etc.) |
Helper method for common parse actions that simply return a literal
value. Especially useful when used with
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Helper parse action for removing quotation marks from parsed quoted strings. To use, add this parse action to quoted string using: quotedString.setParseAction( removeQuotes ) |
DEPRECATED - use new helper method |
Helper to create a validating parse action to be used with start tags created with makeXMLTags or makeHTMLTags. Use withAttribute to qualify a starting tag with a required attribute value, to avoid false matches on common tags such as <TD> or <DIV>. Call withAttribute with a series of attribute names and values. Specify the list of filter attributes names and values as:
For attribute names with a namespace prefix, you must use the second form. Attribute names are matched insensitive to upper/lower case. To verify that the attribute exists, but without specifying a value, pass withAttribute.ANY_VALUE as the value. |
Helper method for constructing grammars of expressions made up of operators working in a precedence hierarchy. Operators may be unary or binary, left- or right-associative. Parse actions can also be attached to operator expressions. Parameters:
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Helper method for defining nested lists enclosed in opening and closing delimiters ("(" and ")" are the default). Parameters:
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. Use the ignoreExpr argument to define expressions that may contain opening or closing characters that should not be treated as opening or closing characters for nesting, such as quotedString or a comment expression. Specify multiple expressions using an Or or MatchFirst. The default is quotedString, but if no expressions are to be ignored, then pass None for this argument. |
Helper method for defining space-delimited indentation blocks, such as those used to define block statements in Python source code. Parameters:
A valid block must contain at least one blockStatement. |
Variables Details |
alphanums
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printables
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unicodeString
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alphas8bit
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