How do you reverse a dictionary?

Question

I'm trying to write a function -- dict_reverse(inputDict) that returns a dictionary that has inputDict's keys and values swapped. (You can assume that no values are repeated in inputDict.)

I'm not really sure how to approach this problem as I am new to dictionaries. I understand their concept and how to use them, but I am stuck as for reversing them.

def dict_reverse(inputDict):
    '''dict_reverse(inputDict) -> dict
    returns dict with keys/values of inputDict swapped'''
    # add my code here

testDict = {'adam':80,'betty':60,'charles':50}
reversedDict = dict_reverse(testDict)
print(reversedDict)
# should output {80:'adam',60:'betty',50:'charles'} in some order

it should output {80:'adam',60:'betty',50:'charles'}

Sorry about that @Austin, meant to include this one: [Python reverse / invert a mapping](https://stackoverflow.com/questions/483666/python-reverse-invert-a-mapping?rq=1) — Yaakov Bressler, Sep 02 '19 at 16:17

score 1 · Accepted Answer · answered Sep 02 '19 at 16:13

Python 3

def dict_reverse(inputDict):
    '''dict_reverse(inputDict) -> dict
    returns dict with keys/values of inputDict swapped'''
    return dict((v,k) for k,v in inputDict.items())

testDict = {'adam':80,'betty':60,'charles':50}
reversedDict = dict_reverse(testDict)
print(reversedDict)

Output {80: 'adam', 60: 'betty', 50: 'charles'}

score 0 · Answer 2 · answered Sep 02 '19 at 16:10

You can use a dict-comprehension and swap the k, v pairs:

def dict_reverse(inputDict):
    return {v: k for k, v in inputDict.items()}

testDict = {'adam': 80, 'betty': 60, 'charles': 50}
reversedDict = dict_reverse(testDict)
print(reversedDict)

Output:

{80: 'adam', 60: 'betty', 50: 'charles'}

How do you reverse a dictionary?

2 Answers2