The evolution of a Python programmer

#Newbie programmer
def factorial(x):
    if x == 0:
        return 1
    else:
        return x * factorial(x - 1)
print factorial(6)

#First year programmer, studied Pascal
def factorial(x):
    result = 1
    i = 2
    while i <= x:
        result = result * i
        i = i + 1
    return result
print factorial(6)

#First year programmer, studied C
def fact(x): #{
    result = i = 1;
    while (i <= x): #{
        result *= i;
        i += 1;
    #}
    return result;
#}
print(fact(6))

#First year programmer, SICP
@tailcall
def fact(x, acc=1):
    if (x > 1): return (fact((x - 1), (acc * x)))
    else:       return acc
print(fact(6))

#First year programmer, Python
def Factorial(x):
    res = 1
    for i in xrange(2, x + 1):
        res *= i
    return res
print Factorial(6)

#Lazy Python programmer
def fact(x):
    return x > 1 and x * fact(x - 1) or 1
print fact(6)

#Lazier Python programmer
f = lambda x: x and x * f(x - 1) or 1
print f(6)

#Python expert programmer
fact = lambda x: reduce(int.__mul__, xrange(2, x + 1), 1)
print fact(6)

#Python hacker
import sys
@tailcall
def fact(x, acc=1):
    if x: return fact(x.__sub__(1), acc.__mul__(x))
    return acc
sys.stdout.write(str(fact(6)) + '\n')

#EXPERT PROGRAMMER
from c_math import fact
print fact(6)

See also: the evolution of a Ruby, JavaScript, PHP, C or Perl programmer, and where this joke started, Fritz Ruehr's The Evolution of a Haskell Programmer (itself a riff on the old "Hello World" Evolution of a Programmer).