Provides a read-write view that groups multiple dictionaries, allowing lookups to fall back through the chain and updates to affect the first mapping.

To combine multiple dictionaries for unified access without merging them, useful for layered configurations or overlays.

When you need to treat several dictionaries as a single mapping, e.g., layering defaults over user settings or combining multiple sources for lookup.

Configuration layering, overlaying defaults over user preferences, combining multiple data sources for lookup, creating read-only views of multiple dicts.

dict1, dict2

• collections
• ChainMap
• dict
• mapping
• update

• dict1
• dict2 can be any mapping objects
• e.g.
• dict
• defaultdict
• ChainMap itself

Assuming updates affect all underlying mappings; forgetting that only the first mapping is mutated.

dict.update() creates a new merged dict; {**dict1, **dict2} creates a new dict; collections.ChainMap provides a live view.

Mutations affect only the first mapping; later mappings remain read-only in the view.

• collections.ChainMap
• dict.update
• {**dict1
• **dict2}
• collections.ChainMap(*maps)

Changes to the first mapping are reflected immediately; changes to later mappings are visible only if they occur before lookup.

Provides a lightweight, non-duplicating view for layered configuration.

Think of stacking transparencies: look through the top sheet first.

Using collections.ChainMap with more than two mappings or custom update behavior