Dictionaries and Tuples

Another application of tuples is to use them as keys in dictionaries. Follow and practice the examples presented in this section in order to understand how tuples can be used with dictionaries.


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):

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)

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.