[dictionary] how to get key by item

[Egor Bolonev]

saluton al ciuj

i know how to get item by key

==================
dict = {10 : 50, 2 : 12, 4 : 43}

print dict[2]

>> 12

but i wonder how to get key by item

print dict[12]

>> 2
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is there a more fast way than that one (my dictionary is really big)
==================
dict = {10 : 50, 2 : 12, 4 : 43}
item = 12
for key in dict.keys():
     if dict[key] == item:
         print key
         break
==================