MNT: theory 2

tacaswell · tacaswell · commit b2f73a69b2aa · 2024-09-17T10:31:56.000-04:00
diff --git a/lib/matplotlib/text.py b/lib/matplotlib/text.py
@@ -66,24 +66,24 @@ def _get_text_metrics_with_cache(renderer, text, fontprop, ismath, dpi):
     """Call ``renderer.get_text_width_height_descent``, caching the results."""
     # Cached based on a copy of fontprop so that later in-place mutations of
     # the passed-in argument do not mess up the cache.
-    func = _get_text_metrics_function(weakref.ref(renderer))
+    func = _get_text_metrics_function(renderer)
     return func(text, fontprop.copy(), ismath, dpi)
 
 
-@functools.lru_cache(25)
-def _get_text_metrics_function(renderer_ref):
-
-    @functools.lru_cache(4096)
-    def _text_metrics(text, fontprop, ismath, dpi):
-        # dpi is unused, but participates in cache invalidation (via the renderer).
-        renderer = renderer_ref()
-        if renderer is None:
-            raise RuntimeError(
-                "You are trying to get the font metrics for a renderer that no "
-                "longer exists.  There is likely a deeper bug someplace else "
-                "as this should never happen."
-            )
-        return renderer.get_text_width_height_descent(text, fontprop, ismath)
+# use mutable default to carry hidden global state
+def _get_text_metrics_function(inp_renderer, _cache=weakref.WeakKeyDictionary()):
+    if (_text_metrics := _cache.get(inp_renderer, None)) is None:
+        renderer_ref = weakref.ref(inp_renderer)
+        @functools.lru_cache(4096)
+        def _text_metrics(text, fontprop, ismath, dpi):
+            # dpi is unused, but participates in cache invalidation (via the renderer).
+            if (lcl_renderer := renderer_ref()) is None:
+                raise RuntimeError(
+                    "Trying to get text metrics for a renderer that no longer exists.  "
+                    "This should never happen and is evidence of a bug elsewhere."
+                    )
+            return lcl_renderer.get_text_width_height_descent(text, fontprop, ismath)
+        _cache[inp_renderer] = _text_metrics
 
     return _text_metrics
 
