multiple attribute based sorting in python (object based and list based)

advanced_sort.py

# sort dates using Objects, and also by lists
# first year wise, then month and finally day wise

class Date:
    def __init__(self, d, m, y):
        self.d = d;
        self.m = m;
        self.y = y;
    
    def __repr__(self):
        return '{}-{}-{}'.format(self.d, self.m, self.y)
    
    def __lt__(self, d2):
        if self.y != d2.y:
            return self.y < d2.y
        elif self.m != d2.m:
            return self.m < d2.m
        else:
            return self.d < d2.d

#object based implementation
dates = []
for _ in range(int(input())):
    d, m, y = map(int, input().split())
    dates.append(Date(d, m, y))
print(sorted(dates))

#simple implementation
d= [[12, 3, 1997], [12, 3, 1992]]
print(sorted(d, key= lambda x: (x[2], x[1], x[0]))) #key returns tuples, which are to be considered for sorting