Make it possible to set new values in Configuration (#863)

opentelemetry-api/src/opentelemetry/configuration/__init__.py

@@ -142,19 +142,18 @@ def __new__(cls) -> "Configuration":
     def __getattr__(self, name: str) -> Optional[ConfigValue]:
         return self._config_map.get(name)
 
-    def __setattr__(self, key: str, val: ConfigValue) -> None:
-        if key == "_config_map":
-            super().__setattr__(key, val)
+    def __setattr__(self, name: str, value: ConfigValue) -> None:
+        if name not in self._config_map.keys():
+            self._config_map[name] = value
         else:
-            raise AttributeError(key)
+            raise AttributeError(name)
 
     def get(self, name: str, default: _T) -> _T:
         """Use this typed method for dynamic access instead of `getattr`
 
         :rtype: str or bool or int or float or None
         """
-        val = self._config_map.get(name, default)
-        return val
+        return self._config_map.get(name, default)
 
     @classmethod
     def _reset(cls) -> None:

opentelemetry-api/tests/configuration/test_configuration.py

@@ -39,7 +39,7 @@ def test_singleton(self) -> None:
             "OPENTELEMETRY_PTHON_TRACEX_PROVIDER": "tracex_provider",
         },
     )
-    def test_environment_variables(self):
+    def test_environment_variables(self) -> None:
         self.assertEqual(
             Configuration().METER_PROVIDER, "meter_provider"
         )  # pylint: disable=no-member
@@ -58,13 +58,16 @@ def test_environment_variables(self):
         "os.environ",  # type: ignore
         {"OPENTELEMETRY_PYTHON_TRACER_PROVIDER": "tracer_provider"},
     )
-    def test_property(self):
+    def test_property(self) -> None:
         with self.assertRaises(AttributeError):
             Configuration().TRACER_PROVIDER = "new_tracer_provider"
 
-    def test_slots(self) -> None:
+    def test_set_once(self) -> None:
+
+        Configuration().XYZ = "xyz"
+
         with self.assertRaises(AttributeError):
-            Configuration().XYZ = "xyz"  # pylint: disable=assigning-non-slot
+            Configuration().XYZ = "abc"  # pylint: disable=assigning-non-slot
 
     def test_getattr(self) -> None:
         # literal access