Cannot work with Stem and Tor

Question

I want to work with Tor through Stem module.The following is my code to get connected with Tor:

import sys
from stem.connection import connect

if __name__ == '__main__':
    controller = connect()

    if not controller:
        sys.exit(1)  # unable to get a connection

    print 'Tor is running version %s' % controller.get_version()
    controller.close()

However, i get following error when running the code:Unable to connect to tor. Are you sure it's running?

I turned on Tor and tested the code again and nothing happened. The problem is this line:

if __name__ == '__main__':
    controller = connect()

Even if I enter the connect() method to Python interpreter I get the error. What is the error and how can I fix it?