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# This is a general factorial function written in Python.
# A factorial is the product of all positive integers <= a given number.
# Works transparently with integers and floating point;
# that is, it returns the same type as its single argument.
# Gives an error for negative or non-integer input values.
def factorial(x):
"Return x! (x factorial)."
if (x < 0 or (x % 1.0) != 0.0):
raise ValueError("Factorial argument must be a positive integer.")
if (x == 0):
return x + 1
d = x
while (x > 2):
x -= 1
temp = d * x
if (temp <= d):
raise ValueError("Factorial result too large.")
d = temp
return d
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