python – Get key by value in dictionary

python – Get key by value in dictionary

mydict = {george: 16, amber: 19}
print mydict.keys()[mydict.values().index(16)]  # Prints george

Or in Python 3.x:

mydict = {george: 16, amber: 19}
print(list(mydict.keys())[list(mydict.values()).index(16)])  # Prints george

Basically, it separates the dictionarys values in a list, finds the position of the value you have, and gets the key at that position.

More about keys() and .values() in Python 3: How can I get list of values from dict?

There is none. dict is not intended to be used this way.

dictionary = {george: 16, amber: 19}
search_age = input(Provide age)
for name, age in dictionary.items():  # for name, age in dictionary.iteritems():  (for Python 2.x)
    if age == search_age:
        print(name)

python – Get key by value in dictionary

If you want both the name and the age, you should be using .items() which gives you key (key, value) tuples:

for name, age in mydict.items():
    if age == search_age:
        print name

You can unpack the tuple into two separate variables right in the for loop, then match the age.

You should also consider reversing the dictionary if youre generally going to be looking up by age, and no two people have the same age:

{16: george, 19: amber}

so you can look up the name for an age by just doing

mydict[search_age]

Ive been calling it mydict instead of list because list is the name of a built-in type, and you shouldnt use that name for anything else.

You can even get a list of all people with a given age in one line:

[name for name, age in mydict.items() if age == search_age]

or if there is only one person with each age:

next((name for name, age in mydict.items() if age == search_age), None)

which will just give you None if there isnt anyone with that age.

Finally, if the dict is long and youre on Python 2, you should consider using .iteritems() instead of .items() as Cat Plus Plus did in his answer, since it doesnt need to make a copy of the list.