Using generators in Python you can do this much much faster :D. #!/usr/bin/env python """ Calculate fibonacci numbers using a generator Usage:

Using generators in Python you can do this much much faster :D. #!/usr/bin/env python """ Calculate fibonacci numbers using a generator Usage: fibonacci.py [options] <N> Arguments: <N> Print all Fibonacci numbers up to <N>-th Options: -h, --help This help """ from docopt import docopt def fibonacci(): """generate fibonacci numbers""" a, b = 0, 1 while 1: yield a a, b = b, a + b if __name__ == '__main__': try: args = docopt(__doc__) fib = fibonacci() for i in range(int(args["<N>"])): print fib.next() except ValueError: print "You must specify valid integer" except KeyboardInterrupt: print "Good-bye" You get something like $ time ./fibonacci.py 46 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181 6765 10946 17711 28657 46368 75025 121393 196418 317811 514229 832040 1346269 2178309 3524578 5702887 9227465 14930352 24157817 39088169 63245986 102334155 165580141 267914296 433494437 701408733 1134903170 real 0m0.038s user 0m0.015s sys 0m0.018s