CODEWITHSUNDEEP
pythondictionarykey
malsatori
malsatori

Reputation: 39

Dictionary type that can be used to return value:key

I am working on a program where I have a dictionary dict['key'] = value, but I would also like to be able to use dict['value'] and have it return the key.

Are there any reversible data structures like this in Python?

I was thinking of adding all of the opposites to my dictionary because all of my relations are 1:1, but I don't think that would be as efficient because I would have twice as many entries as I need.

Upvotes: 2

Views: 72

Answers (2)

Mureinik
Mureinik

Reputation: 311458

I'm not aware of any bidirectional map in python's standard collection library, but you can take a look at the bidict package:

>>> from bidict import bidict
>>> b = bidict(k='v')
>>> b['k']
'v'
>>> b.inv['v']
'k'

Upvotes: 3

Uriel
Uriel

Reputation: 16184

For a single-reverse lookup like this, just use

[k for k in dict if dict[k] == v]

If you use this back-tracking usually, the common way to do it would be to create a reverse dictionary (note that in that case more than one key per value will result in lossy process) - 

rev_dict = {v: k for k, v in dict.items()}

Finally, you might also consider handling your data as tuples of length 2 - like

data = [(a, b), (c, d)]

if one item does not depend on the other.

Upvotes: 2

Related Questions