finding top k largest keys in a dictionary python

return sorted(dictionary, key=dictionary.get, reverse=True)[:10]

Should be at worst O(NlogN) (although heapq proposed by others is probably better) ...

It might also make sense to use a Counter instead of a regular dictionary. In that case, the most_common method will do (approximately) what you want (dictionary.most_common(10)), but only if it makes sense to use a Counter in your API.

O(n log k):

import heapq

k_keys_sorted = heapq.nlargest(k, dictionary)

You could use key keyword parameter to specify what should be used as a sorting key e.g.:

k_keys_sorted_by_values = heapq.nlargest(k, dictionary, key=dictionary.get)