Keyword Variable Arguments (Dictionary)

In the case where we have a variable number or extra set of keyword arguments, these are placed into a dictionary where the "keyworded" argument variable names are the keys, and the arguments are their corresponding values. Why must it be a dictionary? Because a pair of items is given for every argument—the name of the argument and its value—so it is a natural fit to use a dictionary to hold these arguments. Here is the syntax of function definitions which use the variable argument dictionary for extra keyword arguments:

					
def
						function_name([formal_args,][*vargst,] **vargsd):
    function_documentation_string
    function_body_suite

				

To differentiate keyword variable arguments from non-keyword informal arguments, a double asterisk ( ** ) is used. The ** is overloaded so it should not be confused with exponentiation. The keyword variable argument dictionary should be the last parameter of the function definition prepended with the '**'. We now present an example of how to use such a dictionary:

					
def dictVarArgs(arg1, arg2='defaultB', **theRest):
    'display 2 regular args and keyword variable args'
    print 'formal arg1:', dictVarArgs
    print 'formal arg2:', arg2
    for eachXtrArg in theRest.keys():
        print 'Xtra arg %s: %s' % \
            (eachXtrArg, str(theRest[eachXtrArg]))

				

Executing this code in the interpreter, we get the following output:

					
>>> dictVarArgs(1220, 740.0, c='grail'
formal arg1: 1220
formal arg2: 740.0
Xtra arg c: grail
>>>
>>> dictVarArgs(arg2='tales', c=123, d='poe',
a='mystery')
formal arg1: mystery
formal arg2: tales
Xtra arg c: 123
Xtra arg d: poe
>>>
>>> dictVarArgs('one', d=10, e='zoo', men=('freud',
'gaudi'))
formal arg1: one
formal arg2: defaultB
Xtra arg men: ('freud', 'gaudi')
Xtra arg d: 10
Xtra arg e: zoo

				

Both keyword and non-keyword variable arguments may be used in the same function as long as the keyword dictionary is last and is preceded by the non-keyword tuple, as in the following example:

					
def newfoo(arg1, arg2, *nkw, **kw):
    display regular args and all variable args'
    print 'arg1 is:', arg1
    print 'arg2 is:', arg2
    for eachNKW in nkw:
        print 'additional non-keyword arg:', eachNKW
    for eachKW in kw.keys():
        print "additional keyword arg '%s': %s" % \
            (eachKW, kw[eachKW])

				

Calling our function within the interpreter, we get the following output:

					
>>> newfoo('wolf', 3, 'projects', freud=90, gamble=96)
arg1 is: wolf
arg2 is: 3
additional non-keyword arg: projects
additional keyword arg 'freud': 90
additional keyword arg 'gamble': 96