Automatically import all all classes or defined attribute within a module

__init__.py

## IMPORTING PROBLEM:
## - When you want to import a class or any object, attribute from a submodule, you need to specify 
## the filename within the module path
## Example: you want to import class UserAuthentication declared in the file user_authentication.py 
## within the module app.controllers.auth, then: 
## > import UserAuthentication from app.controllers.auth.user_authentication
## INSTEAD, WHY NOT: > import UserAuthentication from app.controllers.auth
## Here is the solution:

import pkgutil
import sys
__all__ = []
for loader, name, is_pkg in pkgutil.walk_packages(__path__):
    if name.startswith('__'):
        continue
    ## 1. replace 'app.controllers.{name}' by your module path
    ## 2. replace 'api' by your class or attribute you need to import
    ## > tips: for attribute you need to import, you can create a function to
    ## > convert the file name from snake case into camel case, which is the importing classname
    module_ = __import__(f'app.controllers.{name}', fromlist=['api']) 
    ## The following step store imported attribute into an array, which can be used dynamically
    __all__.append(getattr(module_, 'api'))