#### Factorial

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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)
1
>>> factorial(6)
720
>>> factorial(0)
1
"""
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)}")