Study of the implementation of factorial

factorial.py

"""Study of the implementation of factorial"""
import pytest
from functools import reduce


def recursive_factorial(n):
    """Given a number n, return the factorial of n"""
    if n == 0:
        return 1
    return n * recursive_factorial(n - 1)


def tail_factorial(n, factorial=1):
    """Factorial implementation with tail recursion"""
    if n == 0:
        return factorial
    return tail_factorial(n-1, n * factorial)


def reduce_factorial(n):
    """Factorial implementation with reduce"""
    numbers = range(n, 0, -1)
    return reduce(lambda factorial, number: factorial * number, numbers, 1)


def for_factorial(n):
    """Factorial implementation with for"""
    factorial = 1
    for number in range(n, 0, -1):
        factorial *= number
    return factorial


def while_factorial(n):
    """Factorial implementation with while"""
    factorial = 1
    while n > 0:
        factorial *= n
        n -= 1
    return factorial


@pytest.mark.parametrize('given, expect', [(0, 1),
                                           (1, 1),
                                           (2, 2),
                                           (3, 6),
                                           (4, 24),
                                           (5, 120)])
def test_factorial(given, expect):
    assert recursive_factorial(given) == expect
    assert tail_factorial(given) == expect
    assert reduce_factorial(given) == expect
    assert for_factorial(given) == expect
    assert while_factorial(given) == expect