Dictionaries and Tuples

12.4 Variable-length argument tuples

Functions can take a variable number of arguments. A parameter name that begins with * gathers arguments into a tuple. For example, printall takes any number of arguments and prints them:

def printall(*args):
    print(args)

The gather parameter can have any name you like, but args is conventional. Here’s how the function works:

>>> printall(1, 2.0, '3')
(1, 2.0, '3')

The complement of gather is scatter. If you have a sequence of values and you want to pass it to a function as multiple arguments, you can use the *operator. For example, divmod takes exactly two arguments; it doesn’t work with a tuple:

>>> t = (7, 3)
>>> divmod(t)
TypeError: divmod expected 2 arguments, got 1

But if you scatter the tuple, it works:

>>> divmod(*t)
(2, 1)

Many of the built-in functions use variable-length argument tuples. For example, max and mincan take any number of arguments:

>>> max(1, 2, 3)
3

But sum does not.

>>> sum(1, 2, 3)
TypeError: sum expected at most 2 arguments, got 3

As an exercise, write a function called sum_all that takes any number of arguments and returns their sum.