Create list of factorials using list comprehension

Question

I\'m trying to build a list of the first ten factorials

[1,1,2,6,24,120,720,5040,40320,362880]

using only list comprehension. Is that possible

Answer 1

Just for fun:

One-liner mega-hack using list comprehension and an auxililary accumulator to reuse previously computed value

s=[];  s=[s[-1] for x in range(1,10) if not aux.append(x*s[-1] if aux else 1)]

result:

[1, 2, 6, 24, 120, 720, 5040, 40320, 362880]

note: The math.factorial answer is the way when elements are random. Here it's faster because we can reuse previous results.

There's also another drawback: the need to store all elements in a list because python does not allow if and assignment like C does. So we have to append to a list and negate the None it returns so if test is True

As I said: fun, but still a hack.

Answer 2

You can use math.factorial():

import math

[math.factorial(n) for n in range(10)]

Output:

>>> import math
>>> 
>>> [math.factorial(n) for n in range(10)]
[1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880]

Answer 3

Your attempt does not work because the list comprehension works element-wise, you cannot refer to lst[i-1] like that. There is a factorial function in math module, however, since you mentioned generators, you can use one like this

def mygenerator():
    total = 1
    current = 1
    while True:
        total *= current
        yield total
        current += 1

factorial = mygenerator()
output = [next(factorial) for i in range(10)]