Module pyparsing :: Class Optional

Class Optional

     object --+        
              |        
  ParserElement --+    
                  |    
ParseElementEnhance --+
                      |
                     Optional

Optional matching of the given expression.

Parameters:

expr - expression that must match zero or more times
default (optional) - value to be returned if the optional expression is not found.

Example:

   # US postal code can be a 5-digit zip, plus optional 4-digit qualifier
   zip = Combine(Word(nums, exact=5) + Optional('-' + Word(nums, exact=4)))
   zip.runTests('''
       # traditional ZIP code
       12345

       # ZIP+4 form
       12101-0001

       # invalid ZIP
       98765-
       ''')

prints:

   # traditional ZIP code
   12345
   ['12345']

   # ZIP+4 form
   12101-0001
   ['12101-0001']

   # invalid ZIP
   98765-
        ^
   FAIL: Expected end of text (at char 5), (line:1, col:6)

Nested Classes

[hide private]

Inherited from ParserElement (private): _FifoCache, _UnboundedCache, _literalStringClass

Instance Methods

[hide private]

__init__(self, expr, default=__optionalNotMatched)
x.__init__(...) initializes x; see help(type(x)) for signature

source code

parseImpl(self, instring, loc, doActions=True)

source code

__str__(self)
str(x)

source code

Inherited from ParseElementEnhance: checkRecursion, ignore, leaveWhitespace, streamline, validate

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

Inherited from ParserElement (private): _parse, _parseCache, _parseNoCache, _setResultsName, _skipIgnorables

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