{"id":"btree-put-is-upsert","text":"`BTree.put()` on an existing key updates the value in-place without incrementing `len(tree)` — it is an upsert, not a blind insert.","truth_value":"IN","source":"entries/2026/05/28/b-tree-storage-engine-tester_test_btree.md","source_url":"","source_hash":"","justifications":[],"dependents":[],"metadata":{"example":"# _insert into leaf: if key exists, update value; else insert new\nidx = bisect_left(keys, key)\nif idx < len(keys) and keys[idx] == key:\n    values[idx] = value  # update\nelse:\n    keys.insert(idx, key); values.insert(idx, value)  # insert"},"explanation":{"steps":[{"node":"btree-put-is-upsert","truth_value":"IN","reason":"premise"}]}}