refactor: Use ChainMap instead of copying dicts

src/mkdocstrings/extension.py

@@ -23,7 +23,8 @@
 ```
 """
 import re
-from typing import Any, Tuple
+from collections import ChainMap
+from typing import Any, Mapping, Tuple
 from xml.etree.ElementTree import XML, Element, ParseError  # noqa: S405 (we choose to trust the XML input)
 
 import yaml
@@ -246,7 +247,7 @@ def get_handler_config(self, handler_name: str) -> dict:
         return {}
 
 
-def get_item_configs(handler_config: dict, config: dict) -> Tuple[dict, dict]:
+def get_item_configs(handler_config: dict, config: dict) -> Tuple[Mapping, Mapping]:
     """
     Get the selection and rendering configuration merged into the global configuration of the given handler.
 
@@ -257,10 +258,8 @@ def get_item_configs(handler_config: dict, config: dict) -> Tuple[dict, dict]:
     Returns:
         Two dictionaries: selection and rendering. The local configurations are merged into the global ones.
     """
-    item_selection_config = dict(handler_config.get("selection", {}))
-    item_selection_config.update(config.get("selection", {}))
-    item_rendering_config = dict(handler_config.get("rendering", {}))
-    item_rendering_config.update(config.get("rendering", {}))
+    item_selection_config = ChainMap(config.get("selection", {}), handler_config.get("selection", {}))
+    item_rendering_config = ChainMap(config.get("rendering", {}), handler_config.get("rendering", {}))
     return item_selection_config, item_rendering_config
 
 

src/mkdocstrings/handlers/python.py

@@ -7,6 +7,7 @@
 import json
 import os
 import sys
+from collections import ChainMap
 from subprocess import PIPE, Popen  # noqa: S404 (what other option, more secure that PIPE do we have? sockets?)
 from typing import Any, List, Optional
 
@@ -65,15 +66,14 @@ class PythonRenderer(BaseRenderer):
     """  # noqa: E501
 
     def render(self, data: Any, config: dict) -> str:  # noqa: D102 (ignore missing docstring)
-        final_config = dict(self.default_config)
-        final_config.update(config)
+        final_config = ChainMap(config, self.default_config)
 
         template = self.env.get_template(f"{data['category']}.html")
 
         # Heading level is a "state" variable, that will change at each step
         # of the rendering recursion. Therefore, it's easier to use it as a plain value
         # than as an item in a dictionary.
-        heading_level = final_config.pop("heading_level")
+        heading_level = final_config["heading_level"]
 
         return template.render(
             **{"config": final_config, data["category"]: data, "heading_level": heading_level, "root": True},
@@ -192,8 +192,7 @@ def collect(self, identifier: str, config: dict) -> Any:
         Returns:
             The collected object-tree.
         """
-        final_config = dict(self.default_config)
-        final_config.update(config)
+        final_config = ChainMap(config, self.default_config)
 
         log.debug("Preparing input")
         json_input = json.dumps({"objects": [{"path": identifier, **final_config}]})