Function factorial

maths/primelib.py:767–794

input: positive integer 'n' returns the factorial of 'n' (n!) >>> factorial(0) 1 >>> factorial(20) 2432902008176640000 >>> factorial(-1) Traceback (most recent call last): ... AssertionError: 'n' must been a int and >= 0 >>> factorial("test") Tra

(n)

def factorial(n):
    """
    input: positive integer 'n'
    returns the factorial of 'n' (n!)

    >>> factorial(0)
    1
    >>> factorial(20)
    2432902008176640000
    >>> factorial(-1)
    Traceback (most recent call last):
        ...
    AssertionError: 'n' must been a int and >= 0
    >>> factorial("test")
    Traceback (most recent call last):
        ...
    AssertionError: 'n' must been a int and >= 0
    """

    # precondition
    assert isinstance(n, int) and (n >= 0), "'n' must been a int and >= 0"

    ans = 1  # this will be return.

    for factor in range(1, n + 1):
        ans *= factor

    return ans


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