datetime не найден пишет

import datetime
import datetime as dt #писал и без import datetime as dt
class knigi():    
    y1=datetime.datetime.today()

    def __init__(self, kniga, name, god):
        """создание книги"""
        self.kniga = kniga
        self.name = name
        self.god = datetime.date(god)

    def gody(self):
        print((y1-self.god).year)

    def days(self):
        print((y1-self.god).day)