Сортировка строк в файле по нескольким символам

class Sorter:
    def __init__(self, input_file):
        self.input_file = input_file
 
    def sort_by_year(self):
        with open(self.input_file, 'r', encoding='utf8') as file:
            sorted_stat = sorted(file)
            print(sorted_stat)
 
 
sort1 = Sorter('log_out.txt')
sort1.sort_by_year()

>>> pprint(sorted(log.split("\n"), key=lambda t: (t[1:5],t[6:8],t[12:14])))
['[2017-05-14 18:46] 1',
 '[2017-05-14 19:43] 2',
 '[2018-01-14 19:44] 1',
 '[2018-02-14 19:49] 3',
 '[2018-05-14 17:40] 1',
 '[2018-05-14 19:39] 1',
 '[2018-05-14 19:42] 1',
 '[2018-05-14 19:45] 2',
 '[2018-05-14 19:47] 2',
 '[2018-05-14 19:48] 2',
 '[2018-09-14 19:38] 4']
>>>

    
def sort_by_month(self):
        with open(self.input_file, 'r', encoding='utf8') as file:
            for line in file:
                pprint(sorted(line.split("\n"), key=lambda t: (t[1:5], t[6:8], t[12:14])))

class Sorter:
    def __init__(self, input_file):
        self.input_file = input_file
 
    def sort_by_year(self):
        with open(self.input_file, 'r', encoding='utf8') as file:
            sorted_stat = sorted(file,  key=lambda t: (t[1:5],t[6:8],t[12:14]))
            print(sorted_stat)
 
 
sort1 = Sorter('input.txt')
sort1.sort_by_year()