初学python问题

学这教程敲代码，运行不了

class SeP():
    def __init__(self):
        # 时间
        self.cook_time = 0
        # 状态
        self.cook_sta = '生的'
        # 调料
        self.cnm = []

    def cook(self, time):
        self.cook_time += time
        if 0 <= self.cook_time <= 3:
            self.cook_sta = '生的'
        elif 3 < self.cook_time <= 5:
            self.cook_sta = '半生不熟'
        elif 5 < self.cook_time <= 8:
            self.cook_sta = '熟了'
        elif 8 < self.cook_time:
            self.cook_sta = '老了'

    def __str__(self):
        return f'这个地瓜被烤过的时间为{self.cook_time},状态是{self.cook_sta}'


dg1 = SeP()
print(dg1)
dg1.cook(3)
print(dg1)

AttributeError: 'SeP' object has no attribute 'cook_time'