settings.py

# -*- coding: utf-8 -*-

import importlib
import os


class ImproperlyConfigured(Exception):
    pass


SETTINGS_MODULE_VAR = 'PROJECT_SETTINGS_MODULE'
VARIABLE_CATALOG_VAR = 'PROJECT_VARIABLE_CATALOG'


class VariableCatalog(object):

    def __init__(self, variables_catalog):
        self.variables = {}
        if os.path.exists(variables_catalog):
            for var in os.listdir(variables_catalog):
                fpath = os.path.join(variables_catalog, var)
                if os.path.isfile(fpath):
                    with open(fpath) as f:
                        self.variables[var] = f.read().strip()

    def __getattr__(self, name):
        try:
            return self.variables[name]
        except KeyError as e:
            raise AttributeError(e)


class Settings(object):

    # Default settings
    DEBUG = 1

    def __init__(self, settings_module, pre=None, post=None):
        self.pre = pre or []
        self.post = post or []
        self.mod = importlib.import_module(settings_module)

    def __getattr__(self, name):
        for obj in self.pre:
            try:
                return getattr(obj, name)
            except AttributeError:
                pass

        try:
            return getattr(self.mod, name)
        except AttributeError:
            pass

        for obj in self.post:
            try:
                return getattr(obj, name)
            except AttributeError:
                pass

        raise AttributeError


pre = []
settings_module = os.environ.get(SETTINGS_MODULE_VAR)
variable_catalog = os.environ.get(VARIABLE_CATALOG_VAR)
if not settings_module:
    raise ImproperlyConfigured(
        'You need to set the {} env variable'.format(
            SETTINGS_MODULE_VAR
        )
    )

if variable_catalog:
    pre.append(VariableCatalog(variable_catalog))
settings = Settings(settings_module, pre=pre)