What is the best way to add entries from 1 dictionary to another?

[mlieqo]

From python 3.9 there are also union operators for dicts! - PEP 584

so this:

d = {'a': 1, 'b': 2}
d.update({'d': 4}

can be also written this way:

d = {'a': 1, 'b': 2}
d |= {'d': 4}