python的形参为可变数据类型的坑

class Bus:
    def __init__(self, passengers=[]):
        self.passengers = passengers

    def pick(self, name):
        self.passengers.append(name)

    def drop(self, name):
        self.passengers.remove(name)


bus1 = Bus([‘a‘, ‘b‘])
print(bus1.passengers)
bus1.pick(‘c‘)
bus1.drop(‘a‘)
print(bus1.passengers)

bus2 = Bus()
bus2.pick(‘a‘)
print(bus2.passengers)

bus3 = Bus()
bus3.pick(‘b‘)
print(bus3.passengers)
print(bus2.passengers)



[‘a‘, ‘b‘]
[‘b‘, ‘c‘]
[‘a‘]
[‘a‘, ‘b‘]
[‘a‘, ‘b‘]