Create directory in python snippet

I've been writing more python these days, and I ran into a need for a method that would recursively create directories if they don't yet exist. I'm sure many other people have written this same thing better, but I thought I'd post it in case anyone out there found it useful:

import os

def CreateDirectory(dir):
  """
  Method that creates the directory structure given.
  This will create directories recursively until the given dir exists.
  """
  if dir[-1] == os.sep:
    dir = dir[0:-1]
  if not os.path.isdir(dir):
    if not os.path.isdir(dir[0:dir.rfind(os.sep)]):
      CreateDirectory(dir[0:dir.rfind(os.sep)])
    os.mkdir(dir)