3.4: Variable-Length Argument Tuples

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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)

Exercise $$\PageIndex{1}$$

Many of the built-in functions use variable-length argument tuples. For example, max and min can 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


Write a function called sumall that takes any number of arguments and returns their sum.

This page titled 3.4: Variable-Length Argument Tuples is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Allen B. Downey (Green Tea Press) .