Dictionary
A mutable key-value store with average O(1) lookup.
- Keys must be hashable and unique.
- Preserves insertion order (Python 3.7+).
- Standard config and lookup container.
When to use: JSON configs, hyperparameters, label-to-id maps, HTTP bodies.
Example: metrics = {"acc": 0.91, "f1": 0.88}; metrics["acc"] returns 0.91.