Module pyparsing :: Class Optional |
[frames] | no frames]

# Class Optional

source code

         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)

Instance Methods
__init__(self, expr, default=_NullToken()) 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__`, `__hash__`, `__invert__`, `__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 `object`: `__delattr__`, `__format__`, `__getattribute__`, `__new__`, `__reduce__`, `__reduce_ex__`, `__setattr__`, `__sizeof__`, `__subclasshook__`

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

Class Variables
| __slotnames__ = ``[``]``
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, expr, default=_NullToken()) (Constructor) | source code
x.__init__(...) initializes x; see help(type(x)) for signature Overrides: object.__init__ (inherited documentation)

### parseImpl(self, instring, loc, doActions=True) | source code
Overrides: ParserElement.parseImpl

### __str__(self) (Informal representation operator) | source code
str(x) Overrides: object.__str__ (inherited documentation)