TheAlgorithms-Python

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"""
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Factorial of a positive integer -- https://en.wikipedia.org/wiki/Factorial
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"""
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def factorial(number: int) -> int:
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    """
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    Calculate the factorial of specified number (n!).
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    >>> import math
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    >>> all(factorial(i) == math.factorial(i) for i in range(20))
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    True
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    >>> factorial(0.1)
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    Traceback (most recent call last):
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        ...
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    ValueError: factorial() only accepts integral values
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    >>> factorial(-1)
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    Traceback (most recent call last):
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        ...
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    ValueError: factorial() not defined for negative values
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    >>> factorial(1)
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    1
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    >>> factorial(6)
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    720
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    >>> factorial(0)
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    1
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    """
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    if number != int(number):
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        raise ValueError("factorial() only accepts integral values")
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    if number < 0:
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        raise ValueError("factorial() not defined for negative values")
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    value = 1
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    for i in range(1, number + 1):
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        value *= i
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    return value
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def factorial_recursive(n: int) -> int:
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    """
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    Calculate the factorial of a positive integer
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    https://en.wikipedia.org/wiki/Factorial
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    >>> import math
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    >>> all(factorial(i) == math.factorial(i) for i in range(20))
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    True
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    >>> factorial(0.1)
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    Traceback (most recent call last):
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        ...
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    ValueError: factorial() only accepts integral values
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    >>> factorial(-1)
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    Traceback (most recent call last):
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        ...
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    ValueError: factorial() not defined for negative values
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    """
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    if not isinstance(n, int):
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        raise ValueError("factorial() only accepts integral values")
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    if n < 0:
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        raise ValueError("factorial() not defined for negative values")
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    return 1 if n in {0, 1} else n * factorial(n - 1)
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if __name__ == "__main__":
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    import doctest
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    doctest.testmod()
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    n = int(input("Enter a positive integer: ").strip() or 0)
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    print(f"factorial{n} is {factorial(n)}")
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