Python Naming Conventions for Dictionaries/Maps/Hashes

values_by_key

1. it is not so confusing as value_key_map: you can't confuse what is value name and what is key name
2. it doesn't name the type directly -- python style naming

I never seem to name them anything like what you proposed (i.e. keeping one way). It just seems to be much more clear when I can find a "proper name" for the hash. It might be "person_details" or "file_sizes" or "album_tracks" etc. (although the last 2 seem to have key_value names, first one a bit less). In rare cases, it will be key_value_map, or value_key_map if it's important that it's a map.

I would never assume any naming scheme for that. Sometimes the values are what you're after, sometimes the keys. My preference is "a natural name".

I think it makes sense to name the dict after the values in the dict, and drop any mention of the key. After all, you are going to be using the dict in situations like values[key] which makes it perfectly clear what the keys are, assuming you named key well.

key_to_value, for example surname_to_salary may be useful when there are closely interrelated maps in code: a to b, b to a, c to b etc.