reduce(lambda x, y: x*y, xrange(a, n))

Last login: Tue Dec  2 21:13:18 on ttys000
 ttys000 /Users/zzz $ python                                                             [0:46]
Python 2.5.1 (r251:54863, Apr 15 2008, 22:57:26) 
[GCC 4.0.1 (Apple Inc. build 5465)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> help(reduce)
Help on built-in function reduce in module __builtin__:

reduce(...)
    reduce(function, sequence[, initial]) -> value
    
    Apply a function of two arguments cumulatively to the items of a sequence,
    from left to right, so as to reduce the sequence to a single value.
    For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates
    ((((1+2)+3)+4)+5).  If initial is present, it is placed before the items
    of the sequence in the calculation, and serves as a default when the
    sequence is empty.

print reduce(lambda x, y: x*y, xrange(a, a+n))

a = float(raw_input("Enter a: "))
n = int(raw_input("Enter n: "))

result = 1
for i in xrange(n):
	result *= a + i
print result

reduce(lambda x, y: x*y, (a+z for z in xrange(n)))