Look Up A Key In A Chain Of Python Dicts?

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 c

Solution 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

Solution 2:

If you're using Python < 3.3, ChainMap isn't available.

This is less elegant, but works:

a= {1:1, 2:2}
b= {3:3, 4:4}

list_dicts= [a, b]

deflookup(key):for i in list_dicts:if key in i:returni[key]raiseKeyErrorlookup(1)# --> 1lookup(4)# --> 4

You add all the dicts to a list, and use a method to look over them.

Solution 3:

May be like below:

if k in d:
    passelif k in e:
    passelif k in f:
    ...