Recursive & Iterative solution of Factorial algorythm

factorial.py

"""
About:
    Script for playing with recursion in python, by calculating factorial of number n

Supported versions:
    >= 2.7

Examples: 
    factorial.py 100
    factorial.py 100 -jt (display just seconds, without results)

Some of the results:
    ➜ python3.7 factorial.py 10 -jt  
    [0.00001s] Recursive
    [0.00001s] Iterative

    ➜ python3.7 factorial.py 100 -jt
    [0.00014s] Recursive
    [0.00003s] Iterative

    ➜ python3.7 factorial.py 1000 -jt
    [0.00275s] Recursive
    [0.00090s] Iterative
    
    ➜ python3.7 factorial.py 10000 -jt
    [0.14668s] Recursive    -> recursion starting to get faster then iterative call on this point
    [0.15047s] Iterative  

    ... getting segmentation fault for 100000 ...
"""

import time, sys
from concurrent.futures import ThreadPoolExecutor

def _print(x):
    try:
        print(x)
    except:
        sys.stderr.write(x)
    

def get(l, index, default=None):
    """
    Safe list accessor
    """
    try:
        return l[index]
    except:
        return default


def stopwatch():
    """
    Count how much time passes until fist call of this function
    until next call
    Example: 
        s = stopwatch()
        [for i in range(20000)]
        print(s("Done!"))
    """

    start_time = time.time()
    return lambda message: "[{:.5f}s] {}".format(time.time() - start_time, message)


# recursive lambda function
fac_recursive = lambda x: 1 if x <= 1 else x * fac_recursive(x-1)


def fac_iterative(x):
    """
    Iterative factorial function
    """

    if x <= 1:
        return 1

    out = 1
    while x > 1:
        x, out = x-1, out * x

    return out


def calc_factorial_recursive(n):
    """
    Calculate factorial recursively
    """

    global just_time
    
    s = stopwatch()
    try:    
        result = fac_recursive(n)
    except:
        result = None    

    return s('Recursive' if just_time else "Recursive: {}\n\n".format(result)) 


def calc_factorial_iterative(n):
    """
    Calculate factorial iteratively
    """

    global just_time
    
    s = stopwatch()    
    result = fac_iterative(n)

    return s('Iterative' if just_time else "Iterative: {}\n\n".format(result))


def main():
    global just_time

    # get args
    n = int(get(sys.argv, 1, 0))
    just_time = get(sys.argv, 2, False) == '-jt'

    # exit if no number passed
    exit("factorial.py - Help\n\nExample: \n\tfactorial.py 10\n\tfactorial.py 10 -jt (to hide results)") if not n else ''

    # execute in parallel 
    with ThreadPoolExecutor(max_workers=3) as executor:
        recursive_future = executor.submit(calc_factorial_recursive, n)
        iterative_future = executor.submit(calc_factorial_iterative, n)

    _print(recursive_future.result())
    _print(iterative_future.result())


if __name__ == '__main__':
    # extend max recursion depth
    sys.setrecursionlimit(100000)
    just_time = False

    main()