python - Comparing two dictionaries Key values and return a new dictionary with the differences -

what want compare 2 dictionaries:

predict = {'eggs': [1,2],'ham': [1,2,3], 'sausage': [1,2,3]} actual = {'eggs': [2], 'ham': [1,2]} 

and return new dictionary of difference:

difference = {'eggs': [1],'ham': [3], 'sausage': [1,2,3]} 

what efficient way (for large amount of data) this? thanks.

you can combine set.difference() , dict comprehension:

>>> predict = {'eggs': [1,2],'ham': [1,2,3]} >>> actual = {'eggs': [2], 'ham': [1,2]} >>> difference = {k: list(set(v).difference(actual[k])) if k in actual else v k, v in predict.items()} {'eggs': [1], 'ham': [3]} 

explanation:

• you iterate on predict key-value pairs
• the new difference dictionary have same keys predict , actual
• but values set difference of current lists
• set(v).difference(actual[k]) - keys same, can access actual[k] , find difference current 1 (which v)
• finally, cast result set difference list have output requested.