Loop Flow when using recursion in python

Question

I'm having concerns on how the loop flow works in Python when Recursion is used (never mind the function, just learning about loop flow)

def factorial(n):
    print("first line")
    if n == 1 or n == 0:
        return 1

    result = n * factorial(n-1)
    print('line after result')
    print('current result is ' + str(result) )
    print('before return result')
    return result

In my example I used factorial(3) and I'm getting it like this:

first line
first line
first line
line after result
current result is 2
before return result
line after result
current result is 6
before return result
6

How come I get line after result three times after result is computed/returned. Am I not supposed to get it only once after the result? How many times does the loop return the result? I don't understand how recursion loop flow works in python. Please help. Thanks

Oleksandr Dashkov · Accepted Answer · 2018-10-02 01:04:36Z

1

You have line after result 2 times(not 3). This line is printed for each return during the recursion calls.

You call factorial(3). Python prints "first line" and runs a function factorial(2).
Python prints "first line" and calls factorial(1).
Python prints "first line" and returns 1;
Gets result from the step 3 and prints line after result;
Gets result from the step 2 and prints line after result;
Gets result from the step 1.

edited Oct 2, 2018 at 1:04

answered Oct 2, 2018 at 0:50

Oleksandr Dashkov

2,9781 gold badge20 silver badges31 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

kw1jybo · Accepted Answer · 2018-10-02 00:54:54Z

0

With the print statement after the case where n==1 return statement, then the print after will only be printed (in your example) for n = 3, and n = 2. For n = 1 the statement will not be printed.

answered Oct 2, 2018 at 0:54

kw1jybo

1521 silver badge8 bronze badges

Collectives™ on Stack Overflow

Loop Flow when using recursion in python

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related