Elegant way to merge dicts without overwriting keys?

[MRAB]

On 2017-05-05 02:23, Malcolm Greene wrote:
> I have a bunch of pickled dicts I would like to merge. I only want to
> merge unique keys but I want to track the keys that are duplicated
> across dicts. Is there a newer dict-like data structure that is fine
> tuned to that use case?
> Short of an optimized data structure, my plan is to convert dict keys to
> sets and compare these sets to determine which keys are unique and can
> be merged and which keys are dupes and should be tracked in that manner.
> At a high level, does this sound like a reasonable approach?
> Thank you,
> Malcolm
> 
(Assuming Python 3.)

Suppose you have a number of dicts:

     dict_1
     dict_2
     dict_3

Collect all of their keys into a list:

     all_keys = list(dict_1) + list(dict_2) + list(dict_3)

How many times does each of the keys occur?

     from collections import Counter
     key_count = Counter(all_keys)

Which keys are unique?

     unique_keys = [key for key in all_keys if key_count[key] == 1]