How this recursive function (factorial function) behaves in Python

Question

I don’t understand how the code behaves after it leaves the recursive function on line 7, fat = n * fatorial(n-1), i.e., how the code assigns the value to the variable n of this line and how is done the calculation of this line where the code assigns its value to the variable fat?

Note: I am self-taught.

#!/usr/bin/python

def fatorial(n):                             #linha1
    print("Calculando o fatorial de %d" % n) #linha2
    if n==0 or n == 1:                       #linha3
        print("Fatorial de %d = 1" % n)      #linha4
        return 1                             #linha5
    else:                                    #linha6
        fat = n * fatorial(n-1)              #linha7
        print(" fatorial de %d = %d" % (n, fat) ) #linha8
    return fat                              #linha9

fatorial(4)

Answer 1

It’s a little complex to explain but I’ll try.

• The factor(4) function is called:
• Factorial(4) execution "hangs" when it needs to calculate fatorial(4-1);
• A new call is made to the function fatorial in another scope with the value of n being 3. This new so-called "lock" in the same place because it is now necessary to calculate the value of fatorial(2). This happens until the execution flow reaches the point of calculating the fatorial(1), which RETURNS the value 1.
• Now the function FRAME fatorial(2) gets the return value to replace fatorial(2-1) and the execution continues.
• The print statement is executed and the returned variable is now the fat with the value of 2.
• Therefore when the function fatorial(2) was executed, the value returned was 2.
• This value will be replaced in the fatorial(3) in row 7, and so on.

To understand how this function works it is necessary to have knowledge about the scope of variables and frames of functions.

Try to access this site here, it will help you understand: link