Reverse the one-to-one mapped dictionary

Question

Suppose there is a dictionary

a = {'a':122,'b':123,'d':333,'e':'233'}

Now I want to revert it as its a one-to-one dictionary so we can do that.

What I have tried:

In [67]: ivd=[(v,k) for (k,v) in a.items()]

In [68]: ivd
Out[68]: [(122, 'a'), (123, 'b'), ('233', 'e'), (333, 'd')]

Now may be some how We can convert this ivd into a dictionary. My questions are

1. How to change this ivd into a dictionary ?
2. Is there any more pythonic solution available to do this? which I think it should be there.

Answer 1

You can use dict constructor:

ivd = dict((v, k) for (k, v) in a.iteritems())

or dict comprehension in python 2.7 or later:

ivd = {v: k for (k, v) in a.items()}

Answer 2

If I understood properly, you're almost there:

>>> ivd={v:k for (k,v) in a.items()}
>>> ivd
{122: 'a', 123: 'b', 333: 'd', '233': 'e'}

(Credit should go to stummjr for this: https://stackoverflow.com/a/11977757/289011 )

Answer 3

Why not just

ivd = {a[key]:key for key in a}

where a is your dict? It seems much simpler. In python, you can directly iterate over the keys of a dict.

Answer 4

Here are two ways how it can be done:

a = {"a": 122, "b": 123, "d": 333, "e": "233"}

expected = {122: "a", 123: "b", 333: "d", "233": "e"}


# Use to invert dictionaries that have unique values
inverted_dict = dict(map(reversed, a.items()))
assert inverted_dict == expected, "1st"

# Use to invert dictionaries that have unique values
inverted_dict = {value: key for key, value in a.items()}
assert inverted_dict == expected, "2nd"

print("PASSED!!!")