switching keys and values in a dictionary in python [duplicate]

Answer 1

You can do it like this:

Function:

def inverse_dict(my_dict):
    updated_dict = {}

for i in my_dict:
    updated_dict[my_dict[i]] = [i]

return updated_dict

Main():

def main():
    year = {'day': 15, 'month': 3, 'year': 2019}
    print(inverse_dict(year))

if __name__ == "__main__":
    main()

Ouput:

{15: ['day'], 3: ['month'], 2019: ['year']}

Answer 2

If the values are not unique this will collide the key space in conversion. Best is to keep the keys in list when switching places

below handles this -

RvsD = dict()
for k,v in MyDict.iteritems():
    RsvD.setdefault(v, []).append(k)

Answer 3

my_dict2 = dict((y,x) for x,y in my_dict.iteritems())

If you are using python 2.7 or 3.x you can use a dictionary comprehension instead:

my_dict2 = {y:x for x,y in my_dict.iteritems()}

Edit

As noted in the comments by JBernardo, for python 3.x you need to use items instead of iteritems

Answer 4

Try this:

my_dict = {2:3, 5:6, 8:9}

new_dict = {}
for k, v in my_dict.items():
    new_dict[v] = k

Answer 5

Use this code (trivially modified) from the accepted answer at Python reverse / invert a mapping:

dict((v,k) for k, v in my_dict.iteritems())

Note that this assumes that the values in the original dictionary are unique. Otherwise you'd end up with duplicate keys in the resulting dictionary, and that is not allowed.

And, as @wim points out, it also assumes the values are hashable. See the Python glossary if you're not sure what is and isn't hashable.

Answer 6

Sometimes, the condition that the values are all unique will not hold, in which case, the answers above will destroy any duplicate values.

The following rolls the values that might be duplicates up into a list:

from itertools import count
dict([(a,[list(d.keys())[i] for i,j in zip(count(), d.values())if j==a in set(d.values())])

I'm sure there's a better (non-list-comp) method, but I had a problem with the earlier answers, so thought I'd provide my solution in case others have a similar use-case.

P.S. Don't expect the dict to remain neatly arranged after any changes to the original! This method is a one-time use only on a static dict - you have been warned!