Module pyparsing :: Class Forward

Class Forward

     object --+        
              |        
  ParserElement --+    
                  |    
ParseElementEnhance --+
                      |
                     Forward

Known Subclasses:

_ForwardNoRecurse

Forward declaration of an expression to be defined later - used for recursive grammars, such as algebraic infix notation. When the expression is known, it is assigned to the Forward variable using the '<<' operator.

Note: take care when assigning to Forward not to overlook precedence of operators. Specifically, '|' has a lower precedence than '<<', so that:

   fwdExpr << a | b | c

will actually be evaluated as:

   (fwdExpr << a) | b | c

thereby leaving b and c out as parseable alternatives. It is recommended that you explicitly group the values inserted into the Forward:

   fwdExpr << (a | b | c)

Converting to use the '<<=' operator instead will avoid this problem.

See ParseResults.pprint for an example of a recursive parser created using Forward.

Instance Methods

__init__(self, other=None)
x.__init__(...) initializes x; see help(type(x)) for signature

source code

__lshift__(self, other)

source code

__ilshift__(self, other)

source code

leaveWhitespace(self)
Disables the skipping of whitespace before matching the characters in the ParserElement's defined pattern. source code

streamline(self)

source code

validate(self, validateTrace=[])
Check defined expressions for valid structure, check for infinite recursive definitions. source code

__str__(self)
str(x)

source code

copy(self)
Make a copy of this ParserElement. source code

Inherited from ParseElementEnhance: checkRecursion, ignore, parseImpl

Inherited from ParserElement: __add__, __and__, __call__, __eq__, __hash__, __invert__, __mul__, __ne__, __or__, __radd__, __rand__, __repr__, __req__, __rmul__, __rne__, __ror__, __rsub__, __rxor__, __sub__, __xor__, addCondition, addParseAction, canParseNext, matches, parseFile, parseString, parseWithTabs, postParse, preParse, runTests, scanString, searchString, setBreak, setDebug, setDebugActions, setFailAction, setName, setParseAction, setResultsName, setWhitespaceChars, split, suppress, transformString, tryParse

Inherited from object: __delattr__, __format__, __getattribute__, __new__, __reduce__, __reduce_ex__, __setattr__, __sizeof__, __subclasshook__

Static Methods
Inherited from `ParserElement`: `enablePackrat`, `inlineLiteralsUsing`, `resetCache`, `setDefaultWhitespaceChars`

Class Variables
Inherited from `ParserElement`: `DEFAULT_WHITE_CHARS`, `packrat_cache`, `packrat_cache_lock`, `packrat_cache_stats`, `verbose_stacktrace`

Properties
Inherited from `object`: `__class__`

Method Details

init(self, other=None)
(Constructor)

source code

x.__init__(...) initializes x; see help(type(x)) for signature

Overrides: object.__init__: (inherited documentation)

leaveWhitespace(self)

source code

Disables the skipping of whitespace before matching the characters in the ParserElement's defined pattern. This is normally only used internally by the pyparsing module, but may be needed in some whitespace-sensitive grammars.

Overrides: ParserElement.leaveWhitespace: (inherited documentation)

streamline(self)

source code

Overrides: ParserElement.streamline

validate(self, validateTrace=`[]`)

source code

Check defined expressions for valid structure, check for infinite recursive definitions.

Overrides: ParserElement.validate: (inherited documentation)

str(self)
(Informal representation operator)

source code

str(x)

Overrides: object.__str__: (inherited documentation)

copy(self)

source code

Make a copy of this ParserElement. Useful for defining different parse actions for the same parsing pattern, using copies of the original parse element.

Example:

   integer = Word(nums).setParseAction(lambda toks: int(toks[0]))
   integerK = integer.copy().addParseAction(lambda toks: toks[0]*1024) + Suppress("K")
   integerM = integer.copy().addParseAction(lambda toks: toks[0]*1024*1024) + Suppress("M")
   
   print(OneOrMore(integerK | integerM | integer).parseString("5K 100 640K 256M"))

prints:

   [5120, 100, 655360, 268435456]

Equivalent form of expr.copy() is just expr():

   integerM = integer().addParseAction(lambda toks: toks[0]*1024*1024) + Suppress("M")

Overrides: ParserElement.copy: (inherited documentation)

Class Forward

__init__(self, other=None) (Constructor)

leaveWhitespace(self)

streamline(self)

validate(self, validateTrace=[])

__str__(self) (Informal representation operator)

copy(self)

init(self, other=None)
(Constructor)

validate(self, validateTrace=`[]`)

str(self)
(Informal representation operator)