Formal and actual parameters in a function in python

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?

Solution 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.

Solution 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.

Solution 3

In Python you defined a function as follow:

• You start the function blocks with the keyword def followed by the function name and parentheses ()

• Any input parameters or arguments should be placed within these parentheses. You can also define parameters inside these parentheses.

In the code you provided. the function factorial takes a parameter n. So for example when I call the function factorial(1+2+3) the expression 1+2+3 get interpreted and becomes 6 and passed in as the function argument to fit parameter n.

So in your function factorial where you called factorial(n+1) you are passing in whatever value generate by n+1 in to factorial as the parameter n

Solution 4

The n in the factorial(n) definition is the formal parameter, as it is the parameter with which the function is being defined. The n-1 in the factorial(n-1) call is an actual parameter, as that is the parameter which the function is being called with.

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