Updated to match latest changes to API
In Google Developer Console inside your app project, on the Credentials section, you must create a new "Service Account" "Client ID", if you have not already. And download the JSON file.
On Google Play Developer Console you have to give permissions to "YOUR_SERVICE_ACCOUNT_EMAIL@developer.gserviceaccount.com" for uploading apks.
Download Google APIs Client Library for Python (google-api-python-client): https://code.google.com/p/google-api-python-client/ or use pip: