diff --git a/maths/factorial_python.py b/maths/factorial_python.py
index ab97cd41e681..b9adfdbaeaff 100644
--- a/maths/factorial_python.py
+++ b/maths/factorial_python.py
@@ -1,21 +1,34 @@
 def factorial(input_number: int) -> int:
     """
-        Non-recursive algorithm of finding factorial of the
-        input number.
-        >>> factorial(1)
-        1
-        >>> factorial(6)
-        720
-        >>> factorial(0)
-        1
+    Calculate the factorial of specified number
+
+    >>> factorial(1)
+    1
+    >>> factorial(6)
+    720
+    >>> factorial(0)
+    1
+    >>> factorial(-1)
+    Traceback (most recent call last):
+        ...
+    ValueError: factorial() not defined for negative values
+    >>> factorial(0.1)
+    Traceback (most recent call last):
+        ...
+    ValueError: factorial() only accepts integral values
     """
 
     if input_number < 0:
-        raise ValueError("Input input_number should be non-negative")
-    elif input_number == 0:
-        return 1
-    else:
-        result = 1
-        for i in range(input_number):
-            result = result * (i + 1)
+        raise ValueError("factorial() not defined for negative values")
+    if not isinstance(input_number, int):
+        raise ValueError("factorial() only accepts integral values")
+    result = 1
+    for i in range(1, input_number):
+        result = result * (i + 1)
     return result
+
+
+if __name__ == '__main__':
+    import doctest
+
+    doctest.testmod()
diff --git a/maths/factorial_recursive.py b/maths/factorial_recursive.py
index f346c65f1962..013560b28b42 100644
--- a/maths/factorial_recursive.py
+++ b/maths/factorial_recursive.py
@@ -1,14 +1,30 @@
-def fact(n):
+def factorial(n: int) -> int:
     """
-    Return 1, if n is 1 or below,
-    otherwise, return n * fact(n-1).
+    Calculate the factorial of specified number
+
+    >>> factorial(1)
+    1
+    >>> factorial(6)
+    720
+    >>> factorial(0)
+    1
+    >>> factorial(-1)
+    Traceback (most recent call last):
+        ...
+    ValueError: factorial() not defined for negative values
+    >>> factorial(0.1)
+    Traceback (most recent call last):
+        ...
+    ValueError: factorial() only accepts integral values
     """
-    return 1 if n <= 1 else n * fact(n - 1)
+    if n < 0:
+        raise ValueError("factorial() not defined for negative values")
+    if not isinstance(n, int):
+        raise ValueError("factorial() only accepts integral values")
+    return 1 if n == 0 or n == 1 else n * factorial(n - 1)
+
 
+if __name__ == '__main__':
+    import doctest
 
-"""
-Show factorial for i,
-where i ranges from 1 to 20.
-"""
-for i in range(1, 21):
-    print(i, ": ", fact(i), sep="")
+    doctest.testmod()