title: Implementing decimal factorial in python
body: <p>I've been trying to implement math functions without the help of <code>math</code> module.
  I used a simple recursive function for factorial:</p>
  <pre><code>def factorial(n):
      if n == 0:
          return 1
      else:
          f = n * factorial(n - 1)
          return f
  </code></pre>
  <p>But recently I found out about the gamma function (which is used to find factorial of decimal numbers). How do I implement it in python?</p>