Dada uma lista de ranqueamento, pegar a primeira ocorrência do maior valor depois da barra /.

test_rank.py

import unittest


def rank1(ranks):
    # by @dunossauro
    return max([(index, value) for index, value in ranks if value], key=lambda x: x[1].split('/')[1])


def rank2(ranks):
    # by @cassiobotaro
    return max(ranks, key=lambda x: int(x[1].split('/')[-1] or 0))


def rank3(ranks):
    # by @viniciusfk9
    return max(ranks, key=lambda x: x[1].split('/')[-1])


class RankTest(unittest.TestCase):
    """
    Dada uma lista de ranqueamento, pegar a primeira ocorrência
    do maior valor depois da barra /.
    Exemplo: [(0, '1/26'), (1, '2/27'), (2, '3/27')]
    Retornar: (1, '2/27')
    """

    def test_1_1(self):
        ranks1 = [(0, '1/26'), (1, '2/27'), (2, '3/27')]
        self.assertEqual(rank1(ranks1), (1, '2/27'))

    def test_2_1(self):
        ranks2 = [(0, ''), (1, '22/27'), (2, '23/26'), (3, '24/27')]
        self.assertEqual(rank1(ranks2), (1, '22/27'))

    def test_3_1(self):
        ranks3 = [(0, ''), (1, '22/27'), (2, '23/29'), (3, '24/29')]
        self.assertEqual(rank1(ranks3), (2, '23/29'))

    def test_4_1(self):
        ranks4 = [(0, '22/27'), (1, '22/26'), (2, '24/27'), (3, '24/27')]
        self.assertEqual(rank1(ranks4), (0, '22/27'))

    def test_1_2(self):
        ranks1 = [(0, '1/26'), (1, '2/27'), (2, '3/27')]
        self.assertEqual(rank2(ranks1), (1, '2/27'))

    def test_2_2(self):
        ranks2 = [(0, ''), (1, '22/27'), (2, '23/26'), (3, '24/27')]
        self.assertEqual(rank2(ranks2), (1, '22/27'))

    def test_3_2(self):
        ranks3 = [(0, ''), (1, '22/27'), (2, '23/29'), (3, '24/29')]
        self.assertEqual(rank2(ranks3), (2, '23/29'))

    def test_4_2(self):
        ranks4 = [(0, '22/27'), (1, '22/26'), (2, '24/27'), (3, '24/27')]
        self.assertEqual(rank2(ranks4), (0, '22/27'))

    def test_1_3(self):
        ranks1 = [(0, '1/26'), (1, '2/27'), (2, '3/27')]
        self.assertEqual(rank3(ranks1), (1, '2/27'))

    def test_2_3(self):
        ranks2 = [(0, ''), (1, '22/27'), (2, '23/26'), (3, '24/27')]
        self.assertEqual(rank3(ranks2), (1, '22/27'))

    def test_3_3(self):
        ranks3 = [(0, ''), (1, '22/27'), (2, '23/29'), (3, '24/29')]
        self.assertEqual(rank3(ranks3), (2, '23/29'))

    def test_4_3(self):
        ranks4 = [(0, '22/27'), (1, '22/26'), (2, '24/27'), (3, '24/27')]
        self.assertEqual(rank3(ranks4), (0, '22/27'))


if __name__ == '__main__':
    unittest.main()

Ou, em Django

ranks = list(snpeffs.values('pk', 'snpeff_rank'))
>>> [{'pk': 2828, 'snpeff_rank': ''},
     {'pk': 2829, 'snpeff_rank': '22/27'},
     {'pk': 2830, 'snpeff_rank': '22/26'},
     {'pk': 2831, 'snpeff_rank': '24/27'},
     {'pk': 2832, 'snpeff_rank': '24/24'}]
max(ranks, key= lambda x: x['snpeff_rank'].split('/')[-1])
>>> {'pk': 2829, 'snpeff_rank': '22/27'}