How to get the key from value in a dictionary in Python?

Question

d[key] = value

but how to get the keys from value?

For example:

a = {"horse": 4, "hot": 10, "hangover": 1, "hugs": 10}
b = 10

print(do_something with 10 to get ["hot", "hugs"])

This is not what a map was made for, it should be the other way around. Why do you need to look for entries by their values? — JDurstberger, Aug 11 '17 at 12:29

score 38 · Accepted Answer · answered Aug 11 '17 at 12:29

38

You can write a list comprehension to pull out the matching keys.

print([k for k,v in a.items() if v == b])

answered Aug 11 '17 at 12:29

John Kugelman

score 11 · Answer 2 · edited Aug 11 '17 at 14:22

Something like this can do it:

for key, value in a.iteritems():
    if value == 10:
        print key

If you want to save the associated keys to a value in a list, you edit the above example as follows:

keys = []
for key, value in a.iteritems():
    if value == 10:
        print key
        keys.append(key)

You can also do that in a list comprehension as pointed out in an other answer.

b = 10 
keys = [key for key, value in a.iteritems() if value == b]

Note that in python 3, dict.items is equivalent to dict.iteritems in python 2, check this for more details: What is the difference between dict.items() and dict.iteritems()?

closest you'll ever get to what OP wants – maestromusica Aug 11 '17 at 12:30 — maestromusica, Aug 11 '17 at 12:30

2 Answers2