Google Maps API. 403. What's the matter?

Question

Google

I need to calculate the distance between two cities in the world with Python backend.
I used the library https://pypi.python.org/pypi/googlemaps/1.0.2. This way of solving my problem required api_key.
I went to https://console.developers.google.com and created a new project as per Google requirements. I then generated an API key (based on my IP) and pasted it into the GoogleMaps example script.
Unfortunately it threw a 403 status. What am I doing wrong?