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Functions can take two different kinds of arguments. A positional argument is just the object itself. A keyword argument is a name assigned to an object.

Example

>>> print('Hello', 'world!', sep=', ')
Hello, world!

The first two strings 'Hello' and world!' are positional arguments. The sep=', ' is a keyword argument.

Note A keyword argument can be passed positionally in some cases.

def sum(a, b=1):
    return a + b

sum(1, b=5)
sum(1, 5) # same as above

Somtimes this is forced, in the case of the pow() function.

The reverse is also true:

>>> def foo(a, b):
...     print(a, b)
...
>>> foo(a=1, b=2)
1 2
>>> foo(b=1, a=2)
2 1

More info
• Keyword only arguments
• Positional only arguments
• /tag param-arg (Parameters vs. Arguments)

A value created inside a function can't be used outside of it unless you return it.

Consider the following function:

def square(n):
    return n * n

If we wanted to store 5 squared in a variable called x, we would do: x = square(5). x would now equal 25.

Common Mistakes

>>> def square(n):
...     n * n  # calculates then throws away, returns None
...
>>> x = square(5)
>>> print(x)
None
>>> def square(n):
...     print(n * n)  # calculates and prints, then throws away and returns None
...
>>> x = square(5)
25
>>> print(x)
None

Things to note
• print() and return do not accomplish the same thing. print() will show the value, and then it will be gone.
• A function will return None if it ends without a return statement.
• When you want to print a value from a function, it's best to return the value and print the function call instead, like print(square(5)).