我试图创建一个应用程序，让学生看到的必修课和选修课的名单使用def关键字在tkinter。这是我运行代码后得到的错误。
Tkinter回调异常

Traceback (most recent call last):
  File "C:\Users\mhm01\anaconda3\lib\tkinter\__init__.py", line 1892, in __call__
    return self.func(*args)
  File "C:\Users\mhm01\AppData\Local\Temp\ipykernel_13464\560191512.py", line 25, in courses
    label3.configure(courses)
  File "C:\Users\mhm01\anaconda3\lib\tkinter\__init__.py", line 1646, in configure
    return self._configure('configure', cnf, kw)
  File "C:\Users\mhm01\anaconda3\lib\tkinter\__init__.py", line 1635, in _configure
    return self._getconfigure1(_flatten((self._w, cmd, '-'+cnf)))
  File "C:\Users\mhm01\anaconda3\lib\tkinter\__init__.py", line 1623, in _getconfigure1
    x = self.tk.splitlist(self.tk.call(*args))
_tkinter.TclError: unknown option "-"