The single star * unpacks the sequence/collection into positional arguments, so you can do this:

def sum(a, b): return a + b values = (1, 2) s = sum(*values)

This will unpack the tuple so that it actually executes as:

s = sum(1, 2)

The double star ** does the same, only using a dictionary and thus named arguments:

values = { 'a': 1, 'b': 2 } s = sum(**values)

You can also combine:

def sum(a, b, c, d): return a + b + c + d values1 = (1, 2) values2 = { 'c': 10, 'd': 15 } s = sum(*values1, **values2)

will execute as:

s = sum(1, 2, c=10, d=15)

Also see section 4.7.4 - Unpacking Argument Lists of the Python documentation.

Additionally you can define functions to take *x and **y arguments, this allows a function to accept any number of positional and/or named arguments that aren't specifically named in the declaration.

Example:

def sum(*values): s = 0 for v in values: s = s + v return s s = sum(1, 2, 3, 4, 5)

or with ** :

def get_a(**values): return values['a'] s = get_a(a=1, b=2) # returns 1

this can allow you to specify a large number of optional parameters without having to declare them.

And again, you can combine: