Shared names and shadowing

Things can get much more tricky when we start naming our parameters and arguments the same names. Let’s modify our earlier example, making it slightly more confusing.

def add_numbers(num1,num2):
    return num1 + num2

num1 = 1
num2 = 100
print(add_numbers(num1,num2))

Though it’s a lot harder to look at, this function call works exactly the same as the function call from the previous step. Only in this case, our arguments are named identically to our parameters. So, our argument num1 (which used to be named x) is passed into our parameter num1. Similarly, our argument num2 (which used to be named y) is passed into our parameter num2. Note that the argument num1 is not the same variable as the parameter num1! The following example illustrate why that is important.

num1 = 5
num2 = 50
print(add_numbers(num2,num1))

In this case, which is even harder to look at, the function call still works exactly the same as above and in the previous step. It is more important than ever to keep arguments and parameters separate, however. This time, our argument num2 is passed into our parameter num1, and our argument num1 is passed into our parameter num2.

This is intentionally confusing to highlight the difference between the variables outside of a function call and inside of a function call. In practical coding, you should avoid using the same parameter and argument names to prevent confusion.