ChainMap

Layer Configuration Safely with Python ChainMap

Applications often build configuration from several sources. Command-line arguments may override environment-derived values, which in turn override built-in defaults. A straightforward implementation copies dictionaries and applies update() repeatedly. That works, but copying hides an important part of the design: configuration is not merely one dictionary. It is a precedence chain of independent sources. Python’s collections.ChainMap makes that relationship explicit. It presents several mappings as one lookup view without merging them first.