Calls

After the def has run, you can call (run) the function in your program by adding parentheses after the function’s name. The parentheses may optionally contain one or more object arguments, to be passed (assigned) to the names in the function’s header:

>>> times(2, 4)            # Arguments in parentheses
8

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This expression passes two arguments to times. As mentioned previously, arguments are passed by assignment, so in this case the name x in the function header is assigned the value 2, y is assigned the value 4, and the function’s body is run. For this function, the body is just a return statement that sends back the result as the value of the call expression. The returned object was printed here interactively (as in most languages, 2 * 4 is 8 in Python), but if we needed to use it later we could instead assign it to a variable. For example:

>>> x = times(3.14, 4)     # Save the result object
>>> x
12.56

Now, watch what happens when the function is called a third time, with very different kinds of objects passed in:

>>> times('Ni', 4)         # Functions are "typeless"
'NiNiNiNi'

This time, our function means something completely different (Monty Python reference again intended). In this third call, a string and an integer are passed to x and y, instead of two numbers. Recall that * works on both numbers and sequences; because we never declare the types of variables, arguments, or return values in Python, we can use times to either multiply numbers or repeat sequences.

In other words, what our times function means and does depends on what we pass into it. This is a core idea in Python (and perhaps the key to using the language well), which we’ll explore in the next section.