Two dictionaries

def union2(dict1, dict2):
    return dict(list(dict1.items()) + list(dict2.items()))

n dictionaries

def union(*dicts):
    return dict(sum(map(lambda dct: list(dct.items()), dicts), []))

or

import itertools

def union(*dicts):
    return dict(itertools.chain(*map(lambda dct: list(dct.items()), dicts)))

Two dictionaries

def union2(dict1, dict2):
    return dict(list(dict1.items()) + list(dict2.items()))

n dictionaries

def union(*dicts):
    return dict(itertools.chain.from_iterable(dct.items() for dct in dicts))

sum has bad performance. See https://mathieularose.com/how-not-to-flatten-a-list-of-lists-in-python/