Configuration 101

There are a couple of principles that will help you to avoid problems when you specify or use your configuration.

Do not access configuration on the module level

Do this:

from app_name.settings import config

def get_redis_client():
    return StrictRedis.from_url(config.REDIS_URL)

Instead of this:

from redis import StrictRedis
from app_name.settings import config

cache_redis = StrictRedis.from_url(config.REDIS_URL)

In this case on each usage the redis client will be re-evaluated, which might be not good for performance reasons.

As an alternative you could have a global Redis instance by using python-lazy-object-proxy:

pip install lazy-object-proxy
import lazy_object_proxy


cache_redis = lazy_object_proxy.Proxy(get_redis_client)

NOTE. Do not forget to clean up shared resources when it is needed, usually on the application / testcase teardown.


Accessing configuration on the module level leads to side-effects on imports, this fact could produce unrelated errors when you run your test suite:

  • Simple unit tests will fail due to lack of configuration options or Vault unavailability;
  • Slow tests due to config initialization and long network calls (they could time out as well);

Having your config access lazy will prevent many for those cases because that code branches won’t be executed on imports and will not affect your test suite.