add docstring explaining factorial function

maths/factorial.py

@@ -3,36 +3,14 @@
 """
 
 
-def factorial(number: int) -> int:
+def factorial(n):
     """
-    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
+    Returns the factorial of a non-negative integer n.
+    Uses recursion.
     """
-    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
+    if n == 0:
+        return 1
+    return n * factorial(n - 1)
 
 
 def factorial_recursive(n: int) -> int: