Combine two dictionaries, concatenate string values?

Question

Related: Is there any pythonic way to combine two dicts (adding values for keys that appear in both)?

I\'d like to merge two string:string dictionaries, and concaten

Answer 1

One can use defaultdict to achieve this:

from collections import defaultdict

a = {'foo': 'bar', 'baz': 'bazbaz'}
b = {'foo': 'baz'}

new_dict = defaultdict(str)
for key, value in a.items():
    new_dict[key] += value
for key, value in b.items():
    new_dict[key] += value

print(new_dict)
# defaultdict(, {'foo': 'barbaz', 'baz': 'bazbaz'})
print(dict(new_dict))
# {'foo': 'barbaz', 'baz': 'bazbaz'}

If there are many dicts to join, we could use itertools.chain.from_iterable:

from collections import defaultdict
from itertools import chain

a = {'foo': 'bar', 'baz': 'bazbaz'}
b = {'foo': 'baz'}
c = {'baz': '123'}
dicts = [a, b, c]

new_dict = defaultdict(str)
for key, value in chain.from_iterable(map(dict.items, dicts)):
    new_dict[key] += value

print(dict(new_dict))
# {'foo': 'barbaz', 'baz': 'bazbaz123'}