Module pyparsing |
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# Module pyparsing

source code

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:

- extra or missing whitespace (the above program will also handle "Hello,World!", "Hello , World !", etc.)
- quoted strings
- embedded comments

Version: 2.1.2

Author: Paul McGuire <ptmcg@users.sourceforge.net>

Classes
| ParseBaseException base exception class for all parsing runtime exceptions
| ParseException exception thrown when parse expressions don't match class; supported attributes by name are:
| ParseFatalException user-throwable exception thrown when inconsistent parse content is found; stops all parsing immediately
| 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
| RecursiveGrammarException exception thrown by `validate()` if the grammar could be improperly recursive
| ParseResults Structured parse results, to provide multiple means of access to the parsed data:
| ParserElement Abstract base level parser element class.
| Token Abstract `ParserElement` subclass, for defining atomic matching patterns.
| Empty An empty token, will always match.
| NoMatch A token that will never match.
| Literal Token to exactly match a specified string.
| Keyword Token to exactly match a specified string as a keyword, that is, it must be immediately followed by a non-keyword character.
| CaselessLiteral Token to match a specified string, ignoring case of letters.
| CaselessKeyword
| Word Token for matching words composed of allowed character sets.
| Regex Token for matching strings that match a given regular expression.
| QuotedString Token for matching strings that are delimited by quoting characters.
| CharsNotIn Token for matching words composed of characters *not* in a given set.
| White Special matching class for matching whitespace.
| GoToColumn Token to advance to a specific column of input text; useful for tabular report scraping.
| LineStart Matches if current position is at the beginning of a line within the parse string
| LineEnd Matches if current position is at the end of a line within the parse string
| StringStart Matches if current position is at the beginning of the parse string
| StringEnd Matches if current position is at the end of the parse string
| 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`).
| 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`).
| ParseExpression Abstract subclass of ParserElement, for combining and post-processing parsed tokens.
| And Requires all given `ParseExpression`s to be found in the given order.
| Or Requires that at least one `ParseExpression` is found.
| MatchFirst Requires that at least one `ParseExpression` is found.
| Each Requires all given `ParseExpression`s to be found, but in any order.
| ParseElementEnhance Abstract subclass of `ParserElement`, for combining and post-processing parsed tokens.
| FollowedBy Lookahead matching of the given parse expression.
| NotAny Lookahead to disallow matching with the given parse expression.
| OneOrMore Repetition of one or more of the given expression.
| ZeroOrMore Optional repetition of zero or more of the given expression.
| Optional Optional matching of the given expression.
| SkipTo Token for skipping over all undefined text until the matched expression is found.
| Forward Forward declaration of an expression to be defined later - used for recursive grammars, such as algebraic infix notation.
| TokenConverter Abstract subclass of `ParseExpression`, for converting parsed results.
| Combine Converter to concatenate all matching tokens to a single string.
| Group Converter to return the matched tokens as a list - useful for returning tokens of `ZeroOrMore` and `OneOrMore` expressions.
| Dict Converter to return a repetitive expression as a list, but also as a dictionary.
| Suppress Converter for ignoring the results of a parsed expression.
| OnlyOnce Wrapper for parse actions, to ensure they are only called once.

Functions
col(loc, strg) Returns current column within a string, counting newlines as line separators. | source code
lineno(loc, strg) Returns current line number within a string, counting newlines as line separators. | source code
line(loc, strg) Returns the line of text containing loc within a string, counting newlines as line separators. | source code
nullDebugAction(*args) 'Do-nothing' debug action, to suppress debugging output during parsing. | source code
traceParseAction(f) Decorator for debugging parse actions. | source code
delimitedList(expr, delim=`'``,``'`, combine=False) Helper to define a delimited list of expressions - the delimiter defaults to ','. | source code
countedArray(expr, intExpr=None) Helper to define a counted list of expressions. | source code
matchPreviousLiteral(expr) 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. | source code
matchPreviousExpr(expr) 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. | source code
oneOf(strs, caseless=False, useRegex=True) 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 `MatchFirst` for best performance. | source code
dictOf(key, value) Helper to easily and clearly define a dictionary by specifying the respective patterns for the key and value. | source code
originalTextFor(expr, asString=True) Helper to return the original, untokenized text for a given expression. | source code
ungroup(expr) Helper to undo pyparsing's default grouping of And expressions, even if all but one are non-empty. | source code
locatedExpr(expr) Helper to decorate a returned token with its starting and ending locations in the input string. | source code
srange(s) Helper to easily define string ranges for use in Word construction. | source code
matchOnlyAtCol(n) Helper method for defining parse actions that require matching at a specific column in the input text. | source code
replaceWith(replStr) Helper method for common parse actions that simply return a literal value. | source code
removeQuotes(s, l, t) Helper parse action for removing quotation marks from parsed quoted strings. | source code
upcaseTokens(s, l, t) Helper parse action to convert tokens to upper case. | source code
downcaseTokens(s, l, t) Helper parse action to convert tokens to lower case. | source code
makeHTMLTags(tagStr) Helper to construct opening and closing tag expressions for HTML, given a tag name | source code
makeXMLTags(tagStr) Helper to construct opening and closing tag expressions for XML, given a tag name | source code
withAttribute(*args, **attrDict) Helper to create a validating parse action to be used with start tags created with `makeXMLTags` or `makeHTMLTags`. | source code
withClass(classname, namespace=`'````'`) Simplified version of `withAttribute` when matching on a div class - made difficult because `class` is a reserved word in Python. | source code
infixNotation(baseExpr, opList, lpar=Suppress:("("), rpar=Suppress:(")")) Helper method for constructing grammars of expressions made up of operators working in a precedence hierarchy. | source code
operatorPrecedence(baseExpr, opList, lpar=Suppress:("("), rpar=Suppress:(")")) Helper method for constructing grammars of expressions made up of operators working in a precedence hierarchy. | source code
nestedExpr(opener=`'``(``'`, closer=`'``)``'`, content=None, ignoreExpr=quotedString using single or double quotes) Helper method for defining nested lists enclosed in opening and closing delimiters ("(" and ")" are the default). | source code
indentedBlock(blockStatementExpr, indentStack, indent=True) Helper method for defining space-delimited indentation blocks, such as those used to define block statements in Python source code. | source code
replaceHTMLEntity(t) Helper parser action to replace common HTML entities with their special characters | source code

Variables
| alphas = ``'``ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz``'``
| nums = ``'``0123456789``'``
| hexnums = ``'``0123456789ABCDEFabcdef``'``
| alphanums = ``'``ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvw``...``
| printables = ``'``0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKL``...``
| empty = `empty`
| lineStart = `lineStart`
| lineEnd = `lineEnd`
| stringStart = `stringStart`
| stringEnd = `stringEnd`
| opAssoc = `_Constants()`
| dblQuotedString = `string enclosed in double quotes`
| sglQuotedString = `string enclosed in single quotes`
| quotedString = `quotedString using single or double quotes`
| unicodeString = `unicode string literal`
| alphas8bit = ``u'``ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖØÙÚÛÜÝÞßàáâãäåæçèéêëìíîï``...``
| punc8bit = ``u'``¡¢£¤¥¦§¨©ª«¬®¯°±²³´µ¶·¸¹º»¼½¾¿×÷``'``
| commonHTMLEntity = `common HTML entity`
| cStyleComment = `C style comment`
| htmlComment = `HTML comment`
| restOfLine = `rest of line`
| dblSlashComment = `// comment`
| cppStyleComment = `C++ style comment`
| javaStyleComment = `C++ style comment`
| pythonStyleComment = `Python style comment`
| commaSeparatedList = `commaSeparatedList`
| anyCloseTag = `</any tag>`
| anyOpenTag = `<any tag>`

Function Details

### col(loc, strg) | source code
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.

### lineno(loc, strg) | source code
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.

### delimitedList(expr, delim=`'``,``'`, combine=False) | source code
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 `combine=True` in the constructor. If `combine` is set to `True`, the matching tokens are returned as a single token string, with the delimiters included; otherwise, the matching tokens are returned as a list of tokens, with the delimiters suppressed.

### countedArray(expr, intExpr=None) | source code
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.

### matchPreviousLiteral(expr) | source code
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 `"1:1"`, but not `"1:2"`. Because this matches a previous literal, will also match the leading `"1:1"` in `"1:10"`. If this is not desired, use `matchPreviousExpr`. Do *not* use with packrat parsing enabled.

### matchPreviousExpr(expr) | source code
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 `"1:1"`, but not `"1:2"`. Because this matches by expressions, will *not* match the leading `"1:1"` in `"1:10"`; the expressions are evaluated first, and then compared, so `"1"` is compared with `"10"`. Do *not* use with packrat parsing enabled.

### oneOf(strs, caseless=False, useRegex=True) | source code
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 `MatchFirst` for best performance. Parameters: strs - a string of space-delimited literals, or a list of string literals caseless - (default=False) - treat all literals as caseless useRegex - (default=True) - as an optimization, will generate a Regex object; otherwise, will generate a `MatchFirst` object (if `caseless=True`, or if creating a `Regex` raises an exception)

### dictOf(key, value) | source code
Helper to easily and clearly define a dictionary by specifying the respective patterns for the key and value. Takes care of defining the `Dict`, `ZeroOrMore`, and `Group` tokens in the proper order. The key pattern can include delimiting markers or punctuation, as long as they are suppressed, thereby leaving the significant key text. The value pattern can include named results, so that the `Dict` results can include named token fields.

### originalTextFor(expr, asString=True) | source code
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. By default, returns astring containing the original parsed text. If the optional `asString` argument is passed as `False`, then the return value is a `ParseResults` containing any results names that were originally matched, and a single token containing the original matched text from the input string. So if the expression passed to `originalTextFor` contains expressions with defined results names, you must set `asString` to `False` if you want to preserve those results name values.

### locatedExpr(expr) | source code
Helper to decorate a returned token with its starting and ending locations in the input string. This helper adds the following results names: locn_start = location where matched expression begins locn_end = location where matched expression ends value = the actual parsed results Be careful if the input text contains `<TAB>` characters, you may want to call `ParserElement.parseWithTabs`

### srange(s) | source code
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 '\x' (\x21, which is a '!' character)
        (\0x## is also supported for backwards compatibility)
      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.)

### replaceWith(replStr) | source code
Helper method for common parse actions that simply return a literal value. Especially useful when used with `transformString()`.

### removeQuotes(s, l, t) | source code
Helper parse action for removing quotation marks from parsed quoted strings. To use, add this parse action to quoted string using:
     quotedString.setParseAction( removeQuotes )

### withAttribute(*args, **attrDict) | source code
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: keyword arguments, as in `(align="right")`, or as an explicit dict with `**` operator, when an attribute name is also a Python reserved word, as in `**{"class":"Customer", "align":"right"}` a list of name-value tuples, as in ( ("ns1:class", "Customer"), ("ns2:align","right") ) For attribute names with a namespace prefix, you must use the second form. Attribute names are matched insensitive to upper/lower case. If just testing for `class` (with or without a namespace), use `withClass`. To verify that the attribute exists, but without specifying a value, pass `withAttribute.ANY_VALUE` as the value.

### infixNotation(baseExpr, opList, lpar=Suppress:("("), rpar=Suppress:(")")) | source code
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: baseExpr - expression representing the most basic element for the nested opList - list of tuples, one for each operator precedence level in the expression grammar; each tuple is of the form (opExpr, numTerms, rightLeftAssoc, parseAction), where: opExpr is the pyparsing expression for the operator; may also be a string, which will be converted to a Literal; if numTerms is 3, opExpr is a tuple of two expressions, for the two operators separating the 3 terms numTerms is the number of terms for this operator (must be 1, 2, or 3) rightLeftAssoc is the indicator whether the operator is right or left associative, using the pyparsing-defined constants `opAssoc.RIGHT` and `opAssoc.LEFT`. parseAction is the parse action to be associated with expressions matching this operator expression (the parse action tuple member may be omitted) lpar - expression for matching left-parentheses (default=Suppress('(')) rpar - expression for matching right-parentheses (default=Suppress(')'))

### operatorPrecedence(baseExpr, opList, lpar=Suppress:("("), rpar=Suppress:(")")) | source code
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: baseExpr - expression representing the most basic element for the nested opList - list of tuples, one for each operator precedence level in the expression grammar; each tuple is of the form (opExpr, numTerms, rightLeftAssoc, parseAction), where: opExpr is the pyparsing expression for the operator; may also be a string, which will be converted to a Literal; if numTerms is 3, opExpr is a tuple of two expressions, for the two operators separating the 3 terms numTerms is the number of terms for this operator (must be 1, 2, or 3) rightLeftAssoc is the indicator whether the operator is right or left associative, using the pyparsing-defined constants `opAssoc.RIGHT` and `opAssoc.LEFT`. parseAction is the parse action to be associated with expressions matching this operator expression (the parse action tuple member may be omitted) lpar - expression for matching left-parentheses (default=Suppress('(')) rpar - expression for matching right-parentheses (default=Suppress(')'))

### nestedExpr(opener=`'``(``'`, closer=`'``)``'`, content=None, ignoreExpr=quotedString using single or double quotes) | source code
Helper method for defining nested lists enclosed in opening and closing delimiters ("(" and ")" are the default). Parameters: opener - opening character for a nested list (default="("); can also be a pyparsing expression closer - closing character for a nested list (default=")"); can also be a pyparsing expression content - expression for items within the nested lists (default=None) ignoreExpr - expression for ignoring opening and closing delimiters (default=quotedString) 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.

### indentedBlock(blockStatementExpr, indentStack, indent=True) | source code
Helper method for defining space-delimited indentation blocks, such as those used to define block statements in Python source code. Parameters: blockStatementExpr - expression defining syntax of statement that is repeated within the indented block indentStack - list created by caller to manage indentation stack (multiple statementWithIndentedBlock expressions within a single grammar should share a common indentStack) indent - boolean indicating whether block must be indented beyond the the current level; set to False for block of left-most statements (default=True) A valid block must contain at least one `blockStatement`.

Variables Details

  ### alphanums Value:
      'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'

  ### printables Value:
      '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!"#$%&\
      '()*+,-./:;<=>?@[\\]^_`{|}~'

  ### alphas8bit Value:
      u'ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõöøùúûüýþÿ'