Enable overriding environ values

src/appsettings/__init__.py

@@ -1,4 +1,5 @@
 """Django AppSettings package."""
+import os
 
 from django.core.exceptions import ImproperlyConfigured
 from django.core.signals import setting_changed
@@ -139,17 +140,20 @@ class AppSettings(metaclass=_Metaclass):
 
     """
 
+    OS_ENVIRON_OVERRIDE_PREFIX = "__DAP_"  # type: str
+
     def __init__(self):
         """
         Initialization method.
 
-        The ``invalidate_cache`` method will be connected to the Django
-        ``setting_changed`` signal in this method, with the dispatch UID
-        being the id of this very object (``id(self)``).
+        The ``invalidate_cache`` and ``manage_environ_invalidation`` methods will be connected to the Django
+        ``setting_changed`` signal in this method, with the dispatch UIDs being method initials and the id of this very
+        object (``id(self)``).
         """
         if self.__class__ == AppSettings:
             raise RuntimeError("Do not use AppSettings class as itself, " "use it as a base for subclasses")
-        setting_changed.connect(self.invalidate_cache, dispatch_uid=id(self))
+        setting_changed.connect(self.invalidate_cache, dispatch_uid="ic" + str(id(self)))
+        setting_changed.connect(self.manage_environ_invalidation, dispatch_uid="mei" + str(id(self)))
         self._cache = {}
 
     def __getattr__(self, item):
@@ -197,6 +201,26 @@ def check(cls):
         if exceptions:
             raise ImproperlyConfigured("\n".join(exceptions))
 
+    def manage_environ_invalidation(self, *, setting, enter, **kwargs):
+        """
+        Manage keys and values in ``os.environ`` on setting change.
+
+        Environ values take precedence over ``django.conf`` values by default. But when we override a setting, we want
+        to take the ``django.conf`` value and therefore we need to remove corresponding key from the ``os.environ``.
+        To be able to restore the original value later, we add a prefix (OS_ENVIRON_OVERRIDE_PREFIX) to the key and then
+        just remove the prefix.
+        """
+        for item in self.settings.keys():
+            if self.settings[item].full_name == setting:
+                setting_override_key = self.OS_ENVIRON_OVERRIDE_PREFIX + setting
+                if enter and setting in os.environ:
+                    os.environ[setting_override_key] = os.environ[setting]
+                    del os.environ[setting]
+                elif not enter and setting_override_key in os.environ:
+                    os.environ[setting] = os.environ[setting_override_key]
+                    del os.environ[setting_override_key]
+                break
+
     def invalidate_cache(self, **kwargs):
         """Invalidate cache. Run when receive ``setting_changed`` signal."""
         self._cache = {}

tests/test_appsettings.py

@@ -2,6 +2,7 @@
 import os
 import tempfile
 from pathlib import Path
+from typing import Dict, cast
 from unittest import mock
 
 import pytest
@@ -773,6 +774,73 @@ class AppConf(appsettings.AppSettings):
         assert "my_int" not in appconf._cache
         assert appconf.my_int == 0
 
+    @mock.patch.dict(os.environ, {"ONE": "Env_1", "TWO": "Env_2", "THREE": "Env_3"})
+    def test_environ_values_invalidation(self):
+        class AppConf(appsettings.AppSettings):
+            one = appsettings.StringSetting()
+            two = appsettings.StringSetting()
+            three = appsettings.StringSetting()
+            four = appsettings.StringSetting(default="Def_4")
+
+        appconf = AppConf()
+        with override_settings(ONE="One", TWO="Two"):
+            assert "ONE" not in os.environ
+            assert "__DAP_ONE" in os.environ
+            assert appconf.one == "One"
+
+            assert "TWO" not in os.environ
+            assert "__DAP_TWO" in os.environ
+            assert appconf.two == "Two"
+
+            assert "THREE" in os.environ
+            assert "__DAP_THREE" not in os.environ
+            assert appconf.three == "Env_3"
+
+            assert "FOUR" not in os.environ
+            assert "__DAP_FOUR" not in os.environ
+            assert appconf.four == "Def_4"
+
+        assert "ONE" in os.environ
+        assert "__DAP_ONE" not in os.environ
+        assert appconf.one == "Env_1"
+
+        assert "TWO" in os.environ
+        assert "__DAP_TWO" not in os.environ
+        assert appconf.two == "Env_2"
+
+        assert "THREE" in os.environ
+        assert "__DAP_THREE" not in os.environ
+        assert appconf.three == "Env_3"
+
+        assert "FOUR" not in os.environ
+        assert "__DAP_FOUR" not in os.environ
+        assert appconf.four == "Def_4"
+
+    @mock.patch.dict(os.environ, {"SETTING": "ONE=Env_1 TWO=Env_2"})
+    def test_environ_nested_setting_invalidation(self):
+        class AppConf(appsettings.AppSettings):
+            setting = cast(
+                Dict[str, str],
+                appsettings.NestedDictSetting(
+                    settings=dict(
+                        one=appsettings.StringSetting(required=True), two=appsettings.StringSetting(default="Def_2"),
+                    ),
+                    required=True,
+                ),
+            )
+
+        appconf = AppConf()
+        assert appconf.setting["one"] == "Env_1"
+        assert appconf.setting["two"] == "Env_2"
+        with override_settings(SETTING={"ONE": "One"}):
+            assert "SETTING" not in os.environ
+            assert "__DAP_SETTING" in os.environ
+            assert appconf.setting["one"] == "One"
+            assert appconf.setting["two"] == "Def_2"
+
+        assert appconf.setting["one"] == "Env_1"
+        assert appconf.setting["two"] == "Env_2"
+
     def test_check(self):
         assert appsettings.AppSettings.check() is None