Python, Recursive Functions and Returns

So, I found out the other other day that if you want to have a value returned when using a recursive function you must include the return line in each instance of the return. Example:

Incorrect way:

 def cleanMyString(self, url):
      returnURL = ''
      if ':' in str(url.encode('utf-8')):
           fixMe = url.replace(':', '_')
           self.clean(fixMe)
      elif '$' in str(url.encode('utf-8')):
           fixMe = url.replace('$', '-')
           self.clean(fixMe)
      else:
            returnURL = url
           return returnURL

The result of this method is None unless the string did not match any of the conditions to re-curse.

Correct way:

 def cleanMyString(self, url):
      returnURL = ''
      if ':' in str(url.encode('utf-8')):
           fixMe = url.replace(':', '_')
           return self.clean(fixMe)
      elif '$' in str(url.encode('utf-8')):
           fixMe = url.replace('$', '-')
           return self.clean(fixMe)
      else:
          returnURL = url
          return returnURL

 

so we can see that instead of calling the function directly we need to put return in front, otherwise we get a return value of None.