[tomku]

The "Python expert" version doesn't run, but it's not hard to fix:

  import operator as op
  import functools as f
  fact = lambda x: f.reduce(op.mul, range(1, x + 1))
  print(fact(6))

If you're using Python 2.x, you can make it a bit shorter due to reduce being in the default namespace:

  import operator as op
  fact = lambda x: reduce(op.mul, xrange(1, x + 1))
  print fact(6)