Two different approaches to writing a function (map vs loop)

Question

SO busy with some code, and have a function which basically takes dictionary where each value is a list, and returns the key with the largest list.

I wrote the following:

def max_list(dic):
    if dic:
        l1 = dic.values()
        l1 = map(len, l1)
        l2 = dic.keys()
        return l2[l1.index(max(l1))]
    else:
        return None

Someone else wrote the following:

def max_list(dic):
    result = None
    maxValue = 0
    for key in dic.keys():
        if len(dic[key]) >= maxValue:
            result = key
            maxValue = len(dic[key])
    return result

Which would be the 'correct' way to do this, if there is one. I hope this is not regarded as community wiki (even though the code works), trying to figure which would be the best pattern in terms of the problem.

Answer 1

Another valid option:

maxkey,maxvalue = max(d.items(),key=lambda x: len(x[1]))

Of the two above, I would probably prefer the explicit for loop as you don't generate all sorts of intermediate objects just to throw them away.

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As a side note, This solution doesn't work particularly well for empty dicts ... (it raises a ValueError). Since I expect that is an unusual case (rather than the norm), it shouldn't hurt to enclose in a try-except ValueError block.

Answer 2

the most pythonic would be max(dic,key=lambda x:len(dic[x])) ... at least I would think ...

maximizing readability and minimizing lines of code is pythonic ... usually