Benchmark a tail call optimisation decorator.

gistfile1.txt

[aliles@macbookpro ~]$ time python2.7 timeit_tco.py 40000
Computed number of length 166714
1.014175 seconds on CPU

real	0m2.109s
user	0m2.094s
sys	0m0.013s

[aliles@macbookpro ~]$ time pypy timeit_tco.py 40000
Computed number of length 166714
3.392062 seconds on CPU

real	0m8.614s
user	0m8.521s
sys	0m0.082s

timeit_tco.py

import sys
import time

class tail_recursive(object):
    """Tail recursion decorator by George Sakkis

    http://code.activestate.com/recipes/496691-new-tail-recursion-decorator/#c3
    """

    def __init__(self, func):
        self.func = func
        self.firstcall = True
        self.CONTINUE = object()

    def __call__(self, *args, **kwd):
        if self.firstcall:
            func = self.func
            CONTINUE = self.CONTINUE
            self.firstcall = False
            try:
                while True:
                    result = func(*args, **kwd)
                    if result is CONTINUE: # update arguments
                        args, kwd = self.argskwd
                    else: # last call
                        return result
            finally:
                self.firstcall = True
        else: # return the arguments of the tail call
            self.argskwd = args, kwd
            return self.CONTINUE

@tail_recursive
def factorial(n, acc=1):
    "calculate a factorial"
    if n == 0:
       return acc
    res = factorial(n-1, n*acc)
    return res

if __name__ == '__main__':
    depth = int(sys.argv[1])
    start = time.clock()
    value = factorial(depth)
    stop = time.clock()
    print 'Computed number of length %d' % len(str(value))
    print stop - start, 'seconds on CPU'