How can I safely create a nested directory?

Question

What is the most elegant way to check if the directory a file is going to be written to exists, and if not, create the directory using Python? Here is what I tried:

Answer 1

import os
if os.path.isfile(filename):
    print "file exists"
else:
    "Your code here"

Where your code here is use the (touch) command

This will check if the file is there if it is not then it will create it.