Problem App Engine app to connect to MySQL in CloudSQL - python-2.7

Question

I've configured SQL second gen. instance and App Engine application (Python 2.7) in one project. I've made necessary settings according to that page.
app.yaml
runtime: python27
api_version: 1
threadsafe: true
env_variables:
CLOUDSQL_CONNECTION_NAME: coral-heuristic-215610:us-central1:db-basic-1
CLOUDSQL_USER: root
CLOUDSQL_PASSWORD: xxxxxxxxx
beta_settings:
cloud_sql_instances: coral-heuristic-215610:us-central1:db-basic-1
libraries:
- name: lxml
version: latest
- name: MySQLdb
version: latest
handlers:
- url: /main
script: main.app
Now as I try to connect from the app (inside Cloud Shell), the error:
OperationalError: (2002, 'Can\'t connect to local MySQL server through socket \'/var/run/mysqld/mysqld.sock\' (2 "No such file or directory")')
Direct connection works:
$ gcloud sql connect db-basic-1 --user=root
was successful...
MySQL [correction_dict]> SHOW PROCESSLIST;
+--------+------+----------------------+-----------------+---------+------+----------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+--------+------+----------------------+-----------------+---------+------+----------+------------------+
| 9 | root | localhost | NULL | Sleep | 4 | | NULL |
| 10 | root | localhost | NULL | Sleep | 4 | | NULL |
| 112306 | root | 35.204.173.246:59210 | correction_dict | Query | 0 | starting | SHOW PROCESSLIST |
| 112357 | root | localhost | NULL | Sleep | 4 | | NULL |
| 112368 | root | localhost | NULL | Sleep | 0 | | NULL |
+--------+------+----------------------+-----------------+---------+------+----------+------------------+
I've authorized IP to connect to the Cloud SQL instance:
Any hints, help?

Answer 1

Google AppEngine Standard provides a unix socket at /cloudsql/[INSTANCE_CONNECTION_NAME] that automatically connects you to your CloudSQL instance. All you need to do is connect to it at that address. For the MySQLDb library, that looks like this:
db = MySQLdb.connect(
unix_socket=cloudsql_unix_socket,
user=CLOUDSQL_USER,
passwd=CLOUDSQL_PASSWORD)
(If you are running AppEngine Flexible, connecting is different and can be found here)