The args and kwargs parameters

We frequently use functions and methods with asterisk or star characters (*) in their definitions, as shown in the following code snippet:

def spam(*args, **kwargs):
    ...

Programmers unfamiliar with Python are often puzzled when they encounter this for the first time. What does the single and double asterisk/star character do?

We'll start with *args. The single * character tells Python that the function takes a variable number (zero or more) of positional parameters.

>>> def countargs(*args):
...     print 'Passed in', len(args), 'args.'
>>> countargs('a', 'b', 'c')
Passed in 3 args.
>>> countargs()
Passed in 0 args.

You can combine normal positional parameters and *args to require some arguments. The os.path.join method, for example, requires at least one positional argument. Its signature is os.path.join(a, *p).

>>> import os
>>> os.path.join('a',...