App initialization utilizes import and decorator side effects

[Glutexo]

The application initialization script uses and import with a side effect. The app.validators module is imported, which uses the jsonschema.draft4_format_checker decorator. It has a side effect of globally registering the validation function. That itself is not a very good thing, but it’s how this external library behaves.

Moreover this all happens not when the app is created (by the create_app function), but when the app module is imported. That makes the app module import itself having a side effect. No no no.

• Remove the decorator side effect
• Remove the import side effect

The decorators can be resolved by using them as a plain function. It doesn’t modify the original function in any way, it just registers it in the module.

# app.validators
@draft4_format_checker.checks('uuid')
…
def verify_uuid_format(uuid_str):
    …

def register_validators():
    validations = (
        "uuid": verify_uuid_format
        …
    )
    for name, func in validations:
        validator = draft4_format_checker.checks(name)
        validator(function)
…

# app
…
from app.validators import register_validators
…
def create_app(config_name):
    …
    register_validators()
    …
…