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12.4: 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):

    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 min can 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.

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