CODEWITHSUNDEEP
pythondictionary
sdasdadas
sdasdadas

Reputation: 25156

Using multiple keys for one value in a Python dictionary

I have a Python dictionary that uses integers as keys

d[7] = ...

to reference custom objects:

c = Car()
d[7] = c

However, each of these custom objects also has a string identifier (from a third party). I want to be able to access the objects using both an integer or a string. Is the preferred way to use both keys in the same dictionary?

d[7] = c
d["uAbdskmakclsa"] = c

Or should I split it up into two dictionaries? Or is there a better way?

Upvotes: 0

Views: 1281

Answers (3)

abarnert
abarnert

Reputation: 366133

It really depends on what you're doing.

If you get the different kinds of keys from different sources, so you always know which kind you're looking up, it makes more sense, conceptually, to use separate dictionaries.

On the other hand, if you need to be able to handle keys that could be either kind, it's probably simpler to use a single dictionary. Otherwise, you need to write code like that uses type-switching, or tries one dict and then tries the other on KeyError, or something else ugly.

(If you're worried about efficiency, it really won't make much difference either way. It's only a very, very tiny bit faster to look things up in a 5000-key dictionary as in a 10000-key dictionary, and it only costs a very small of extra memory to keep two 5000-key dictionaries than one 10000-key dictionary. So, don't worry about efficiency; do whichever makes sense. I don't have any reason to believe you are worried about efficiency, but a lot of people who ask questions like this seem to be, so I'm just covering the bases.)

Upvotes: 4

pyrocumulus
pyrocumulus

Reputation: 9300

It's a fairly specific situation, I doubt there is any 'official' preference on what to do in this situation. I do however, feel that having keys of multiple types is 'dirty', although I can't really think of a reason why it is.

But since you state that the string keys come from a third party, that alone might be a good reason to split off to another dictionary. I would split as well. You never know what the future might bring and this method is easier to maintain. Also less error prone if you think of type safety.

For setting values in your dictionaries you can then use helper methods. This will make adding easier and prevent you from forgetting to add/update to one of the dictionaries.

Upvotes: 1

perreal
perreal

Reputation: 98118

I would use two dicts. One mapping 3rd party keys to integer keys and another one mapping integer keys to objects. Depending on which one you use more frequently you can switch that of course.

Upvotes: 1

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