Python - Opposite of dictionary search

Question

>>>Dictionary[key]

The above statement returns the first corresponding value of the 'key' from the 'Dictionary' but is there a function that does the opposite, i.e. search for the key by it's value

Answer 1

Just iterate over the dictionary items and check for the value with your string. If it matches then print it's corresponding key.

>>> d = {'foo':1,'bar':2}
>>> for k,v in d.items():
        if v == 1:
            print(k)


foo

Answer 2

You can write simple lambda for this:

d={"a":5, "bf": 55, "asf": 55}

search_key = lambda in_d, val: (k for k,v in in_d.items() if v == val)

for k in search_key(d, 55):
    print(k)

# since the lambda returns generator expression you can simply print
# the keys as follows:

print(list(search_key(d, 55)))  
# or get the key list
key_list = list(search_key(d, 55))

Gives:

asf
bf

Answer 3

There's no single function, but it's easy to get the (possibly multiple) keys for a particular value:

>>> d = {'a': 0, 'b': 1, 'c': 2, 'd': 3, 'e': 4, 'f': 0, 'g': 1}
>>> [k for k, v in d.items() if v == 1]
['b', 'g']

Answer 4

i don't think you can, but you can do this

In [3]: dict_1 = {1:"one", 2:"two"}

In [4]: for number, alphabet in dict_1.items():
   ...:     if alphabet == "two":
   ...:         print number
   ...: 

Answer 5

For this you can work with .keys() and .values(), which will return a list of keys or values respectivley. These lists can be easily iterated over and searched.

An example with a simple dictionary:

>>> D1 = {'A':1, 'B':2, 'C':1}
>>> D1['A']
1

>>> for key in D1.keys():
        if D1[key] == 1:
            print(key)
C
A

As Padraic Cunningham pointed out, a key must be unique, but a value does not, so you run into problems when you have multiple keys that match 1 value.

Answer 6

Perhaps it's too straightforward...

def val2key(dict, val):
    for k, v in dict.items():
        if v == val:
            return k
    return None         

Answer 7

Trivial, using list comprehensions:

>>> d = {'a': 1, 'b': 2, 'c': 1}
>>> l = [k for k, v in d.items() if v == 1]
>>> l
['c', 'a']

Answer 8

Use a list comprehension and substitute the name of your dictionary and the desired value.

keys = [k for k, v in my_dict.items() if v == my_value]