CODEWITHSUNDEEP
pythonpython-3.x
Bob
Bob

Reputation: 756

Python recursion timings in return statement

I am currently trying to time recursions of factorials and I cannot find a way around printing every factorial in each recursion step. Now I have tried printing it just in the return statement which would solve my problem, but that just ended up in a mess of wall of text with timings being fragmented.

EDIT: I should mention that I am trying to get the cumulative timings of the whole process and not fragmented results like I have below with the print statement.

I tried something like:

return (str(n) + '! = ' + (str(FactResult)) +  
                   ' - Runtime = %.9f seconds' % (end-start))

But here is what I have below as of now.

import time
def factorial(n):
"""Factorial function that uses recursion and returns factorial of
number given."""
start = time.clock()
if n < 1:
    return 1
else:
    FactResult = n * factorial(n - 1)
    end = time.clock()
    print(str(n) + '! - Runtime = %.9f seconds' % (end-start))
    return FactResult

Upvotes: 0

Views: 130

Answers (2)

pepr
pepr

Reputation: 20762

It seems to work fine after fixing the indentation and minor (cosmetic) changes:

import time

def factorial(n):
    """Factorial function that uses recursion and returns factorial of number given."""

    start = time.clock()
    if n < 1:
        return 1
    else:
        FactResult = n * factorial(n - 1)
        end = time.clock()
        print(str(n) + '! =', FactResult, '- Runtime = %.9f seconds' % (end-start))
        return FactResult

factorial(10)

It prints for me... without printing the result value:

c:\tmp\___python\BobDunakey\so12828669>py a.py
1! - Runtime = 0.000001440 seconds
2! - Runtime = 0.000288474 seconds
3! - Runtime = 0.000484790 seconds
4! - Runtime = 0.000690225 seconds
5! - Runtime = 0.000895181 seconds
6! - Runtime = 0.001097736 seconds
7! - Runtime = 0.001294052 seconds
8! - Runtime = 0.001487008 seconds
9! - Runtime = 0.001683804 seconds
10! - Runtime = 0.001884920 seconds

... and with printing the value:

c:\tmp\___python\BobDunakey\so12828669>py a.py
1! = 1 - Runtime = 0.000001440 seconds
2! = 2 - Runtime = 0.001313252 seconds
3! = 6 - Runtime = 0.002450827 seconds
4! = 24 - Runtime = 0.003409847 seconds
5! = 120 - Runtime = 0.004300708 seconds
6! = 720 - Runtime = 0.005694598 seconds
7! = 5040 - Runtime = 0.006678577 seconds
8! = 40320 - Runtime = 0.007579038 seconds
9! = 362880 - Runtime = 0.008463659 seconds
10! = 3628800 - Runtime = 0.009994826 seconds

EDIT

For the cumulative timing, you have to measure outside the call. Otherwise you are not able to capture the start time. It is also more natural:

import time

def factorial(n):
    """Factorial function that uses recursion and returns factorial of number given."""

    if n < 1:
        return 1
    else:
        return n * factorial(n - 1)


n = 10

start = time.clock()
result = factorial(n)
end = time.clock()

print(str(n) + '! =', result, '- Runtime = %.9f seconds' % (end-start))

It prints:

c:\tmp\___python\BobDunakey\so12828669>py a.py
10! = 3628800 - Runtime = 0.000007200 seconds

Upvotes: 1

Iliyan Bobev
Iliyan Bobev

Reputation: 3108

Move the "end = time.clock()" and the print statement right before the "return 1" in the block that catches n<1. This is the last execution at the biggest depth of the recursion stack, so all you will miss is the backing up out of it. To get the most proper result, you should follow the suggestion of NullUserException and time outside the recursion method.

Upvotes: 0

Related Questions