Incremental Module Loader

Proposes a injection pattern for your modules. Each module is simply a callable which takes other named modules as arguments. It is very simple with less than 40 statements of code and allows a great deal of flexibility while still removing frequent boilerplate we had to write on each of our projects.

This module is used by our SpinHub App (https://www.spinhub.ca) which is currently in development. It is the main building block of our module/service based architecture.

Use-Case 1: Modularize a flask app

You have an auth service, a database service and an blueprint creator function. How do you hook all of these together while keeping good separation of concerns and allowing injection of mocked services ? Let's see:

from incremental_module_loader import IncrementalModuleLoader

from flask import request, jsonify

class RequestParsingModule(object):
    def get_authorization_header(self):
        return request.headers.get('Authorization', None)

class MyAuthModule(object):
    def __init__(self, config, request_parser):
        self.url = config['AUTH_URL']
        self.request_parser = request_parser
    
    def get_user_id_from_token(self):
        header = self.request_parser.get_authorization_header()
        pass # Extract user id from header token...

class MyDatabaseModule(object):
    def __init__(self, config, auth):
        self.db_uri = config['SQLALCHEMY_DATABASE_URI']
        self.auth = auth

    def get_user(self):
        user_id = self.auth.get_user_id_from_token()
        pass # Retrieve user data from database...

# Note the name of the arguments here:
def route_app(app, config, database):

    @app.route('/userinfo')
    def userinfo():
        # This triggers the auth verification from the header extracted from the request parser
        user = database.get_user()
        return jsonify(user.dump())
        # ...


def create_app():
    app = # (...) Standard app creation with config loading

    module_loader = IncrementalModuleLoader()

    # First init the modules with already created objects:
    module_loader.update(
        app=app,
        config=app.config
    )

    # Then load in order ("incrementally")
    # Make sure to specify a CALLABLE object (function or class)
    # The module_loader will call the parameter with the modules it is asking as parameters.
    module_loader.load(request_parser=RequestParsingModule)
    module_loader.load(auth=MyAuthModule)
    module_loader.load(database=MyDatabaseModule)

    # Can be loaded anonymously, returns nothing.
    module_loader.load(route_app)

    # There you have it !

Creators

Created by Tack Verification, a company dedicated to reducing operational costs related to hardware systems verification. https://www.tackv.ca