Is there a better way to merge two dicts of sets?

user_3943868 0
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I am using this code to merge one dict into another - if a key exists, it should merge the values from both dicts:

source_dict = defaultdict(set)
target_dict = defaultdict(set)

def merge_dict(source_dict, target_dict):
    for source_key in source_dict:
        if source_key in target_dict:
            target_dict[source_key].update(source_dict[source_key])
        else:
            target_dict[source_key] = source_dict[source_key]

Is there a way to optimize the merge_dict function above? For example, to make it more concise or more efficient?

defaultdict dictionary python
2 Answers

You are using defaultdicts. So you don't need the if/else... Just do:

def merge_dict(source_dict, target_dict):
    for source_key, source_value in source_dict.items():
        target_dict[source_key].update(source_value)

If the source_key is not in target_dict, an empty set will be created and immediately updated. That's exactly the use-case for defaultdicts...

user_60458000

You could wirte it as an update from a comprehension:

from collections import defaultdict

source_dict = defaultdict(set,{'a':{1,2,3},'b':{4,5,6}})
target_dict = defaultdict(set,{'b':{5,6,7},'c':{8,9}})

target_dict.update((k,s|target_dict[k]) for k,s in source_dict.items())

print(target_dict)
# defaultdict(<class 'set'>, {'b': {4, 5, 6, 7}, 'c': {8, 9}, 'a': {1, 2, 3}})
user_52375600
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