diff --git a/.jules/bolt.md b/.jules/bolt.md
new file mode 100644
index 0000000000..954473e674
--- /dev/null
+++ b/.jules/bolt.md
@@ -0,0 +1,4 @@
+
+## 2024-05-24 - Optimize list comprehensions with walrus operator
+ **Learning:** List comprehensions with redundant function calls (like `input_str.find(char)`) cause the function to be evaluated twice, which is an anti-pattern that slows down processing, especially for O(n) string scanning.
+ **Action:** Use the Python 3.8+ walrus operator (`:=`) to compute and bind the result once, e.g., `[idx for char in chars if (idx := input_str.find(char)) != -1]`.
diff --git a/helpers/dirty_json.py b/helpers/dirty_json.py
index 8b731bee47..ab099bf784 100644
--- a/helpers/dirty_json.py
+++ b/helpers/dirty_json.py
@@ -349,5 +349,5 @@ def _peek(self, n):
 
     def get_start_pos(self, input_str: str) -> int:
         chars = ["{", "[", '"']
-        indices = [input_str.find(char) for char in chars if input_str.find(char) != -1]
+        indices = [idx for char in chars if (idx := input_str.find(char)) != -1]
         return min(indices) if indices else 0