Input parameters

At the beginning of this chapter, we saw that a function can take input parameters. Before we delve into all possible type of parameters, let's make sure you have a clear understanding of what passing a parameter to a function means. There are three key points to keep in mind:

• Argument passing is nothing more than assigning an object to a local variable name
• Assigning an object to an argument name inside a function doesn't affect the caller
• Changing a mutable object argument in a function affects the caller

Let's look at an example for each of these points.

Argument passing

Take a look at the following code. We declare a name, x, in the global scope, then we declare a function, func(y), and finally we call it, passing x:

# key.points.argument.passing.py
x = 3

def func(y):
    print(y)
func(x)  # prints: 3

When func is called with x, within its local scope, a name, y, is created, and it's pointed to the same object x is pointing to. This is better clarified by the following figure...