在应用程序上下文之外获取配置变量

Question

I've extracted several of my sqlalchemy models to a separate and installable package (../lib/site-packages), to use across several applications. So I only need to:

from models_package import MyModel

from any application needing access to these models.

Everything is ok so far, except I cannot find a satisfactory way of getting several application dependent config variables used by some of the models, which may vary from application to application. So some model need to be aware of some variables, where previously I've used the application they were in.

Neither

current_app.config['XYZ']

or

config = LocalProxy(lambda: current_app.config['XYZ'])

have worked ( outside of application context errors) so I'm stuck right now. Maybe this is poor programming and/or design on my behalf, so how do clear this up? There must be some way, but I haven't reasoned myself toward it yet.

SOLUTION:

Avoiding setting items that would occur on module load (like a constant containing an api key), both of the above should work, and they do. Anything not using those in the context of model-in-the-application use will of course error, methods returning the values you need should be good.

Answer 1

well, since current_app can be a proxy of your flask program when the blueprint is registered, and that is done at run-time, you can't use it in your models_package modules. (app tries to import models_package , and models_package requires app's configs to initalize things- thus import fails)

one option would be doing circular imports :

assuming everything is in 'App' module:

__init__.py

import flask

application = flask.Flask(__name__)
application.config = #load configs

import models_package

models_package.py

from App import application
config = application.config

or create your own config object, but that somehow doubles complexity:

models_package.py

import flask

config = flask.config.Config(defaults=flask.Flask.default_config)

#pick one of those and apply the same config initialization as you do in 
#your __init__.py
config.from_pyfile(..) #or
config.from_object(..) #or
config.from_envvar(..) 

Answer 2

If you are using a configuration pattern utilising classes and inheritance as described here , you could simply import your config classes with their respective properties and access them anywhere you want:

class Config(object):
    IMPORT = 'ME'
    DEBUG = False
    TESTING = False
    DATABASE_URI = 'sqlite:///:memory:'

class ProductionConfig(Config):
    DATABASE_URI = 'mysql://user@localhost/foo'

class DevelopmentConfig(Config):
    DEBUG = True

class TestingConfig(Config):
    TESTING = True

Now, in your foo.py :

from config import Config

print(Config.IMPORT) # prints 'ME'