django_conf.py

from typing import Any

from django.conf import settings
from django.utils.module_loading import import_string


def import_from_string(val, setting_name):
    """
    Attempt to import a class from a string representation.
    """
    try:
        return import_string(val)
    except ImportError as e:
        msg = "Could not import '%s' for setting '%s'. %s: %s." % (val, setting_name, e.__class__.__name__, e)
        raise ImportError(msg)


def perform_import(val, setting_name):
    """
    If the given setting is a string import notation,
    then perform the necessary import or imports.
    """
    if val is None:
        return None
    elif isinstance(val, str):
        return import_from_string(val, setting_name)
    elif isinstance(val, (list, tuple)):
        return [import_from_string(item, setting_name) for item in val]
    return val


class SimpleAppSettings:
    defaults = {}
    transforms = {}
    import_strings = []

    def __init__(self, setting_name, defaults=None, import_strings=None, transforms=None) -> None:
        super().__init__()
        self.defaults = defaults or self.defaults
        self.user_settings = getattr(settings, setting_name, {})
        self.import_strings = import_strings or self.import_strings
        self.transforms = transforms or self.transforms
        self._cached_attrs = set()

    def __getattr__(self, attr):
        if attr not in self.defaults:
            raise AttributeError("Invalid setting: '%s'" % attr)
        try:
            # Check if present in user settings
            val = self.user_settings[attr]
        except KeyError:
            # Fall back to defaults
            val = self.defaults[attr]
        if attr in self.transforms:
            val = self.transforms[attr](val)
        # Coerce import strings into classes
        if attr in self.import_strings:
            val = perform_import(val, attr)

        # Cache the result
        self._cached_attrs.add(attr)
        setattr(self, attr, val)
        return val

    def __dir__(self):
        return [*self.defaults.keys()]


class AppSettings(SimpleAppSettings):
    def __init__(self, setting_name, defaults=None, import_strings=None, transforms=None) -> None:
        d = {k: v for k, v in self.__class__.__dict__.items() if not k.startswith('_')}
        d.pop('defaults', None)
        d.pop('transforms', None)
        d.pop('import_strings', None)
        d.update(defaults or {})
        super().__init__(setting_name, defaults=d, import_strings=import_strings, transforms=transforms)

    def __getattribute__(self, name: str) -> Any:
        if name != 'defaults' and name in self.defaults:
            return self.__getattr__(name)
        return object.__getattribute__(self, name)