Remove Thing.application_config and move deepcopy to ThingServerInterface.

This keeps the application config as a server property, which I think is clearer. Also, we now deep copy it every time it's needed, rather than in `Thing.__init__`.

It may be nice in the future to swap deepcopy for some kind of freezing method, but that's for a future PR, and probably not worth an issue.

Author: rwb27

src/labthings_fastapi/thing.py

@@ -9,7 +9,6 @@
 from typing import TYPE_CHECKING, Any, Optional
 from typing_extensions import Self
 from collections.abc import Mapping
-from copy import deepcopy
 import logging
 import os
 import json
@@ -83,8 +82,6 @@ class Thing:
     _thing_server_interface: ThingServerInterface
     """Provide access to features of the server that this `.Thing` is attached to."""
 
-    application_config: Mapping[str, Any] | None
-
     def __init__(self, thing_server_interface: ThingServerInterface) -> None:
         """Initialise a Thing.
 
@@ -101,9 +98,6 @@ def __init__(self, thing_server_interface: ThingServerInterface) -> None:
             `.create_thing_without_server` which generates a mock interface.
         """
         self._thing_server_interface = thing_server_interface
-        # Create a deepcopy of the configuration so if one Thing mutates the config
-        # it cannot propagate.
-        self.application_config = deepcopy(thing_server_interface.application_config)
         self._disable_saving_settings: bool = False
 
     @property

src/labthings_fastapi/thing_server_interface.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 from concurrent.futures import Future
+from copy import deepcopy
 import os
 from typing import (
     TYPE_CHECKING,
@@ -159,7 +160,7 @@ def path(self) -> str:
     @property
     def application_config(self) -> Mapping[str, Any] | None:
         """The custom application configuration options from configuration."""
-        return self._get_server().application_config
+        return deepcopy(self._get_server().application_config)
 
     def get_thing_states(self) -> Mapping[str, Any]:
         """Retrieve metadata from all Things on the server.

tests/test_thing.py

@@ -27,8 +27,10 @@ def test_thing_can_access_application_config():
     thing2 = server.things["thing2"]
 
     # Check both Things can access the application config
-    assert thing1.application_config == {"foo": "bar", "mock": True}
-    assert thing1.application_config == thing2.application_config
+    thing1_config = thing1._thing_server_interface.application_config
+    thing2_config = thing2._thing_server_interface.application_config
+    assert thing1_config == {"foo": "bar", "mock": True}
+    assert thing1_config == thing2_config
     # But that they are not the same dictionary, preventing mutations affecting
     # behaviour of another thing.
-    assert thing1.application_config is not thing2.application_config
+    assert thing1_config is not thing2_config