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python/s/factorial.md

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+---
+title: Factorial
+type: snippet
+language: python
+tags: [math,recursion]
+cover: succulent-11
+dateModified: 2020-09-15T16:13:06+03:00
+---
+
+Calculates the factorial of a number.
+
+- Use recursion.
+- If `num` is less than or equal to `1`, return `1`.
+- Otherwise, return the product of `num` and the factorial of `num - 1`.
+- Throws an exception if `num` is a negative or a floating point number.
+
+```py
+def factorial(num):
+  if not ((num >= 0) and (num % 1 == 0)):
+    raise Exception("Number can't be floating point or negative.")
+  return 1 if num == 0 else num * factorial(num - 1)
+```
+
+```py
+factorial(6) # 720
+```