Parameters vs. arguments

Parameters and arguments are very closely related concepts, and you may hear the terms being used interchangeably. It is important to understand the difference to gain a full understanding of how function calls work, however. By definition, a parameter is a variable that an argument is stored in when a function is called. In other words, when you call a function, you pass in an argument which is stored in the parameter that was outlined when the function was defined. Let’s get a better understanding of this concept through an example.

def return_plus_one(param):
    return (param+1)

This is a very simple function which returns its parameter plus 1. In any function definition, the parameters are defined in the first line, between the parenthesis after the function name. In this case, param is the parameter. Now, let’s say we call this function.

a = 5
return_plus_one(a)

When we call the function return_plus_one() , we use the variable a as the argument. An argument can be any object, which includes (but isn’t limited to) an int, float, string, list, or boolean. Anything that can be stored in a variable can be used as an argument.

def print_and_return(param):
    print(param)
    return

In print_and_return(), param is, of course, a parameter for the function print_and_return(). However, param is also an argument for the print() function call within print_and_return(). Though it may get a little confusing, it is important to separate what is inside a function call from what is outside of the function call, as will be illustrated in this lesson.

In class, we called a parameters formal arguments and we called arguments actual arguments.