Look up a key in a chain of Python dicts?

Question

Is there a built-in way in Python to look up a key k in a dict d and, if the key is not present, look it up instead in another dict e?

Can this be extended to an arbitrarily long chain of dicts d => e => f => ...?

Answer 1

You could use a collections.ChainMap:

from collections import ChainMap

d = ChainMap({'a': 1, 'b': 2}, {'b': 22}, {'c': 3})
print(d['c'])
print(d['b'])

This would output:

3
2

Notice that the lookup for key 'b' was satisfied by the first dictionary in the map and the remaining dicts where not searched.

ChainMap was introduced in Python 3.3