【Python】listのappend

import json
class MyClass:
    def __init__(self, a, b):
        self.group = []
        self.a = a
        self.b = b

    def add(self):
        c = self.a + self.b
        self.group.append(c)
        print(self.group)

obj = MyClass(2, 4)
obj.add()
obj.add()

$ python3 test.py
[6]
[6, 6]