what are keys in hashmaps python code example

Example: hash map in python

>>> from collections import ChainMap
>>> dict1 = {'one': 1, 'two': 2}
>>> dict2 = {'three': 3, 'four': 4}
>>> chain = ChainMap(dict1, dict2)

>>> chain
ChainMap({'one': 1, 'two': 2}, {'three': 3, 'four': 4})

# ChainMap searches each collection in the chain
# from left to right until it finds the key (or fails):
>>> chain['three']
3
>>> chain['one']
1
>>> chain['missing']
KeyError: 'missing'