fruit = ['banana', 'melon', 'lime', 'somereallylongfruit', 'kiwi']

print [i for i in fruit if len(i) == max([len(j) for j in fruit])][0]
somereallylongfruit


print [len(j) for j in fruit]
[6, 5, 4, 19, 4]

fruit = ['a', 'melon', 'kiwis', 'grape', 'lime']
print [i for i in fruit if len(i) == max([len(j) for j in fruit])][0]
melon