Python 属性错误：'；非类型'；对象没有属性'；db'；

我已将所有列和表添加到Sqlite数据库中。我能做些什么来纠正这个错误吗？

我注意到的唯一一个

db

的地方是

engine=config.db

：检查/显示您的配置。从sqlalchemy.testing.schema导入表中删除

，只需使用
sqlalchemy
中的
表即可（您已经导入）。
Traceback (most recent call last):
  File "/Users/knutjorgenbjuland/PycharmProjects/assignment_7_1/main.py", line 13, in <module>
    Column('course_id',Integer,ForeignKey('courses.id')))
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/sqlalchemy/testing/schema.py", line 26, in Table
    if exclusions.against(config._current, "mysql"):
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/sqlalchemy/testing/exclusions.py", line 452, in against
    config
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/sqlalchemy/testing/exclusions.py", line 356, in __call__
    if pred(config):
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/sqlalchemy/testing/exclusions.py", line 273, in __call__
    engine = config.db
AttributeError: 'NoneType' object has no attribute 'db'

 from sqlalchemy import Table, Column, Integer, String, ForeignKey
 from sqlalchemy import create_engine
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.orm import relationship, sessionmaker

 # declarative_base() returns the base class used for table descriptions
 from sqlalchemy.testing.schema import Table

 Base = declarative_base()

 students_course_table = Table('student_course',Base.metadata,
                          Column('student_id',Integer,ForeignKey('students.id')),
                          Column('course_id',Integer,ForeignKey('courses.id')))