my first real program blows up, can someone tell me why?

[Jerry F. Davis]

I read the tutorial and tried a variation on what i saw there. and it
blew up, with a integer overflow. can someone tell me why?

Looks like a nice language so far. One that I would want to teach my 15
year old son. I wouldn't want to teach him pearl, because it is so
cryptic in nature.

thanks.

I am running python 1.5.2 on linux.

Here is the program:

#!/usr/bin/python

# why does this give me a integer overflow?

import sys

def fib(n):
	print 'a Fibonacci series up to', n
	a, b = 0, 1
	while b < n:
		print b,
		a, b = b, a+b


l = len(sys.argv)
if l == 1:
	print """
	fibonacci3: print out a fibonacci sequence.
	usage:	fibonacci3 value
	"""
else:
	x = sys.argv[1]
	print 'now doing fib(', x, ')'
	fib(x)