>>> s = [['2019', 1], ['2018', 0], ['2017', 'qwe']]
>>> s.sort()
>>> s
[['2017', 'qwe'], ['2018', 0], ['2019', 1]]
>>> s = [['2019', 1], ['2019', 0], ['2019', 'qwe']]
>>> s.sort()
Traceback (most recent call last):
File "<pyshell#16>", line 1, in <module>
s.sort()
TypeError: '<' not supported between instances of 'str' and 'int'