import sys 

def fib(n): 
if (n < 2): 
return n 
else: 
return fib(n - 1) + fib(n - 2) 

def main(): 
limit = int(sys.argv) 
print fib(limit) 
main() 

With generator 

def fib(): 
a, b = 0, 1 
while True: 
yield a 
a, b = b, a + b