Implement a data structure(dict-like), you can get value by index or key. Just like data[index] or data[key].

dict-like.py

import unittest

def get_of_data(data, key):
    if type(key) is int:
        if key < len(data[1]):
            k = data[1][key]
            return data[0][k]
        raise IndexError('The index is out of range.')
    elif type(key) is str:
        return data[0][key]

def set_of_data(key, value, data=None):
    if type(key) not in [int, str]:
        raise TypeError('Unsupport type! Only support int or str.')
    if data is not None:
        data[0].update({key: value})
        index = len(data[1]) # get the index of next item
        data[1].update({index: key})
    else:
        data = [{key: value}, {0: key}]
    return data

class TestDataStructureMethods(unittest.TestCase):
    def test_set_of_data(self):
        d = set_of_data('a', 3)
        self.assertEqual(d, [{'a': 3}, {0: 'a'}])
        d = set_of_data('b', 5, d)
        self.assertEqual(d, [{'a': 3, 'b': 5}, {0: 'a', 1: 'b'}])
        with self.assertRaises(TypeError):
            set_of_data((), 10, d)
            
    def test_get_of_data(self):
        d = [{'a': 3, 'c': 9, 'b': 5, 'd': 1}, {0: 'a', 2: 'b', 3: 'c', 4: 'd'}]
        self.assertEqual(get_of_data(d, 'c'), 9)
        self.assertEqual(get_of_data(d, 2), 5)
        with self.assertRaises(IndexError):
            get_of_data(d, 9)
            
if __name__ == '__main__':
    unittest.main()