List as value in dictionary, get key of longest list

Question

Give a dictionary like this

testDict = {76: [4], 32: [2, 4, 7, 3], 56: [2, 58, 59]}

How do I get the key of the longest list? In this case

Answer 1

Use max:

>>> max(testDict, key=lambda x:len(testDict[x]))
32

If multiple keys contain the longest list:

I want to get multiple keys then.

>>> testDict = {76: [4], 32: [2, 4, 7, 3], 56: [2, 58, 59], 10: [1, 2, 3, 4]}
>>> mx = max(len(x) for x in testDict.itervalues())
>>> [k for k, v in testDict.iteritems() if len(v)==mx]
[32, 10]