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factorial_iterative.py
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30 lines (26 loc) · 875 Bytes
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# factorial of a positive integer -- https://en.wikipedia.org/wiki/Factorial
def factorial(n: int) -> int:
"""
>>> 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 n != int(n):
raise ValueError("factorial() only accepts integral values")
if n < 0:
raise ValueError("factorial() not defined for negative values")
value = 1
for i in range(1, n + 1):
value *= i
return value
if __name__ == "__main__":
n = int(input("Enter a positive integer: ").strip() or 0)
print(f"factorial{n} is {factorial(n)}")