Formal and actual parameters in a function in python [duplicate]

Question

I'm kind of confused on how to identify the formal and actual parameters in a recursive function. For example in this block of code for getting the factorial of a number:

def factorial(n):
    if n == 1:
       return 1
    else:
       return n * factorial(n-1)

Is "factorial(n-1)" the formal parameter since it is inside the function itself? Or is it the actual parameter because it assigned a value for the function. Also, is the "factorial(n)" the formal parameter as well?

Answer 1

A formal parameter, i.e. a parameter, is in the function definition. An actual parameter, i.e. an argument, is in a function call.

So n here:

def factorial(n):

Is a formal parameter.

And n - 1 (or rather, the value it evaluates to) here:

   return n * factorial(n-1)

Is an "actual parameter", i.e. an argument.

Answer 2

The formal parameter is the name you use to refer to the actual parameter (aka argument) to the function. In your definition of factorial, n is the formal parameter. In the call to factorial, the value of the expression n - 1 serves as the actual parameter which inside the recursive call is bound to (again) the formal parameter n.