⚡ Bolt: Optimize dictionary defaults in hot loops

.jules/bolt.md

@@ -0,0 +1,3 @@
+## 2024-04-27 - [Avoid setdefault with eager initialization in hot loops]
+**Learning:** Using `dict.setdefault(key, complex_initialization())` inside a hot loop forces the Python interpreter to eagerly evaluate the default value (such as a list comprehension with `Fraction(0)`) on every single iteration, even if the key already exists. This can cause severe performance degradation, especially when dealing with computationally expensive object creation or large iterations.
+**Action:** Replace `dict.setdefault` with explicit `if key not in dict:` checks when the default value involves function calls, list comprehensions, or object instantiations. This ensures the default value is only evaluated when necessary (i.e., on cache miss).

src/geometry/hull_kv.py

@@ -17,7 +17,6 @@
     HardmaxResult,
     NumberLike,
     ValueLike,
-    _as_fraction,
     _coerce_key,
     _coerce_value,
     _normalize_number,
@@ -205,10 +204,14 @@ def _rebuild_if_needed(self) -> None:
         total_value_sum = [Fraction(0) for _ in range(self._value_width or 0)]
 
         for index, (key, value) in enumerate(self._entries):
-            bucket = aggregates.setdefault(
-                key,
-                {"value_sum": [Fraction(0) for _ in value], "count": 0, "entry_indices": []},
-            )
+            # Performance optimization: explicit check to avoid eagerly evaluating default dict
+            if key not in aggregates:
+                aggregates[key] = {
+                    "value_sum": [Fraction(0) for _ in value],
+                    "count": 0,
+                    "entry_indices": [],
+                }
+            bucket = aggregates[key]
             for coord_index, coord in enumerate(value):
                 bucket["value_sum"][coord_index] += coord
                 total_value_sum[coord_index] += coord