MODULE-SCOPED CODE TO CONFIGURE DEPLOYMENT ENVIRONMENTS.

db_connection.py

# db_connection.py
from __main__ import TESTING

class TestingDatabase:
    def __init__(self):
        print("Connecting to DEV database")

class RealDatabase:
    def __init__(self):
        print("Connecting to PROD database")

Database = [RealDatabase, TestingDatabase][TESTING]

dev_main.py

# dev_main.py
TESTING = True

import db_connection

db = db_connection.Database()

prod_main.py

# prod_main.py
TESTING = False

import db_connection

db = db_connection.Database()

For example, say that I want to run a program in a web server container and give it access to a database. Every time I want to modify my program’s code, I need to run a server container, the database schema must be set up properly, and my program needs the password for access. This is a very high cost if all I’m trying to do is verify that a one-line change to my program works correctly.

The best way to work around such issues is to override parts of a program at startup time to provide different functionality depending on the deployment environment. For example, I could have two different main files—one for production and one for development: