Get the Key(s) corresponding to max(value) in python dict

Question

Let's consider sample dictionaries of (key, value) pairs as follows:

 dict1 = {'a' : 10, 'x' : 44, 'f': 34, 'h':89, 'j': 90, 'd': 28, 'g' : 90}
 dict2 = {'a' : 10, 'x' : 44, 'f': 34, 'h':89, 'j': 90, 'd': 28}

Of all the values in the dictionaries, 90 is the highest. I need to retrieve the key or keys that correspond to it.

What are the possible ways to get this done? Which is the most efficient one, and why?

Note:

1. Keys and/or values are not in order for the dictionary. The program keeps adding new (key, value) pairs to the dictionary.

2. There might be more than one key for max(value)

   a) If a dict has only one key corresponding to max(value), then the result should be just a string (i.e. Key). Example: dict2 above should return 'j'

   b) If a dict has more than one key corresponding to max(value), then the result should be list of strings (i.e. keys). Example: dict1 above should return ['j', 'g']

Answer 1

Use max() and list comprehension:

>>> dic = {'a' : 10, 'x' : 44, 'f': 34, 'h':89, 'j': 90, 'd': 28,"k":90}
>>> maxx = max(dic.values())             #finds the max value
>>> keys = [x for x,y in dic.items() if y ==maxx]  #list of all 
                                                   #keys whose value is equal to maxx
>>> keys
['k', 'j']

Create a function:

>>> def solve(dic):
    maxx = max(dic.values())
    keys = [x for x,y in dic.items() if y ==maxx] 
    return keys[0] if len(keys)==1 else keys
... 
>>> solve({'a' : 10, 'x' : 44, 'f': 34, 'h':89, 'j': 90, 'd': 28})
'j'
>>> solve({'a' : 10, 'x' : 44, 'f': 34, 'h':89, 'j': 90, 'd': 28, 'g' : 90})
['g', 'j']

Answer 2

You can do:

maxval = max(dict.iteritems(), key=operator.itemgetter(1))[1]
keys = [k for k,v in dict.items() if v==maxval]