Create Calculate-factorial.md

Author: SamratBarai

snippets/python/math-and-numbers/Calculate-factorial.md

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+---
+title: Calculate Factiorial of a number
+description: Calculates factorial of a given number using recursive function
+author: SamratBarai
+tags: math,factorial,recursive-function
+---
+
+```py
+def factorial(n):
+    if type(n) != int or n < 0: raise ValueError("Invalid value of input: '" + str(n) + "'") # Raises an error for invalid input
+    if n == 0 or n == 1: return 1 # Returns 1 if n is 0 or 1
+    else: return n * factorial(n-1) # Recall the factorial function
+```
+
+# Usage:
+print(factorial(4)) # Returns 24
+print(factorial(-3)) # Returns type error for invalid inputs