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"""

Factorial of a positive integer -- https://en.wikipedia.org/wiki/Factorial

"""

def factorial(number: int) -> int:

"""

Calculate the factorial of specified number (n!).

>>> import math

>>> all(factorial(i) == math.factorial(i) for i in range(20))

True

>>> factorial(0.1)

Traceback (most recent call last):

...

ValueError: factorial() only accepts integral values

>>> factorial(-1)

Traceback (most recent call last):

...

ValueError: factorial() not defined for negative values

>>> factorial(1)

>>> factorial(6)

720

>>> factorial(0)

"""

if number != int(number):

raise ValueError("factorial() only accepts integral values")

if number < 0:

raise ValueError("factorial() not defined for negative values")

value = 1

for i in range(1, number + 1):

value *= i

return value

def factorial_recursive(n: int) -> int:

"""

Calculate the factorial of a positive integer

https://en.wikipedia.org/wiki/Factorial

>>> import math

>>> all(factorial(i) == math.factorial(i) for i in range(20))

True

>>> factorial(0.1)

Traceback (most recent call last):

...

ValueError: factorial() only accepts integral values

>>> factorial(-1)

Traceback (most recent call last):

...

ValueError: factorial() not defined for negative values

"""

if not isinstance(n, int):

raise ValueError("factorial() only accepts integral values")

if n < 0:

raise ValueError("factorial() not defined for negative values")

return 1 if n in {0, 1} else n * factorial(n - 1)

if __name__ == "__main__":

import doctest

doctest.testmod()

n = int(input("Enter a positive integer: ").strip() or 0)

print(f"factorial{n} is {factorial(n)}")

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