get Key by value, dict, python

Question

How can I get a key from a value?

my dict:

countries = {
        "Normal UK project" : "1",
        "UK Omnibus project" : "1-Omni",
        "Nordic project" : ["11","12","13","14"],
        "German project" : "21",
        "French project" : "31"
        }

my semi functioning code:

for k, v in countries.items():
    if "1" in v:
        print k

expected output:

Normal UK project

actual output:

French project
UK Omnibus project
German project
Normal UK project

How can I fix my code?

Asked By: Boosted_d16

||

Source

Answer 1

def keys_of_value(dct, value):
    for k in dct:
        if isinstance(dct[k], list):
            if value in dct[k]:
                return k
        else:
            if value == dct[k]:
                return k

assert keys_of_value(countries, "12") == "Nordic project"
assert keys_of_value(countries, "1")  == "Normal UK project"

If you want me to shorten it a little bit, I might do

from operator import eq, contains

def keys_of_value(dct, value, ops = (eq, contains)):
    for k in dct:
        if ops[isinstance(dct[k], list)](dct[k], value):
            return k

assert keys_of_value(countries, "12") == "Nordic project"
assert keys_of_value(countries, "1") == "Normal UK project"

Answered By: thefourtheye

Answer 2

The problem is that the types of the values in the dictionary are not the same, making it much more difficult to use the dictionary, not only in this scenario. While Python allows this, you really should consider unifying the types in the dictionary, e.g. make them all lists. You can do so in just one line of code:

countries = {key: val if isinstance(val, list) else [val] 
                        for key, val in countries.items()}

Now, each single string is wrapped into a list and your existing code will work correctly.

Alternatively, if you have to use the dictionary in it’s current form, you can adapt your lookup function:

for k, v in countries.items():
    if "1" == v or isinstance(v, list) and "1" in v:
        print k

Answered By: tobias_k

Answer 3

Your semi-functioning code is returning the other values because with entries like:

    "Normal UK project" : "1",

..then "1" in v checks if the string contains the “1” character, whereas with entries like:

    "Nordic project" : ["11","12","13","14"],

..then it will check if the list contains an element “1”.

The in operator works on both strings and lists, but in a different manner:

>>> "1" in "123"
True
>>> "1" in ["123", "blah"]
False
>>> "1" in ["1", "blah"]
True

Ideally your data would be more consistent – all lists, or all strings:

countries = {
        "Normal UK project" : ["1"],
        "UK Omnibus project" : ["1-Omni"],
        "Nordic project" : ["11","12","13","14"],
        "German project" : ["21"],
        "French project" : ["31"]
        }

for k, v in countries.items():
    if "1" in v:
        print k

Answered By: dbr

Answer 4

I personally think using in and the function values is easier.

print 1 in {1:"123", 2:"blah"}
print "blah" in {1:"123", 2:"blah"}.values()

Output is:

True
True

Answered By: Ehsan Ab

Answer 5

c={} – any dict

a(value) – need know this key

key=list(c.keys())[list(c.values()).index(a)]

Answered By: Юра Панарин

Answer 6

def get_Value(dic,value):
    for name in dic:
        if dic[name] == value:
            return name

Answered By: Raj Damani

Answer 7

The following code provide another and short version of getting dictionary keys by some value, by using list comprehensions and dic.items():

keys_have_value = [k for k,v in dic.items() if v=="1"]

Answered By: Serjik

get Key by value, dict, python

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