Added factorial_recursive.py with doctests and descriptive parameter …

maths/factorial_recursive.py

@@ -0,0 +1,37 @@
+"""
+Recursive factorial implementation.
+
+Reference: https://en.wikipedia.org/wiki/Factorial
+"""
+
+
+def factorial(number: int) -> int:
+    """
+    Calculate the factorial of a non-negative integer recursively.
+
+    Parameters:
+        number (int): A non-negative integer whose factorial is to be calculated.
+
+    Returns:
+        int: The factorial of the input number.
+
+    Raises:
+        ValueError: If the input number is negative.
+
+    Examples:
+        >>> factorial(0)
+        1
+        >>> factorial(1)
+        1
+        >>> factorial(5)
+        120
+    """
+    if number < 0:
+        raise ValueError("number must be non-negative")
+    if number <= 1:
+        return 1
+    return number * factorial(number - 1)
+
+
+if __name__ == "__main__":
+    print(factorial(5))