为什么 from tkinter import * 不导入 Tkinter 的消息框？

Question

I am learning Python, and as I try some code using tkinter I hit this issue:

I import all the definitions of tkinter with the line:

from tkinter import *

Then I try to open a message box:

messagebox.showinfo(message='My message')

But when I run the program, if this line must be executed, I get the message:

Traceback (most recent call last):
  File ...
  ...
NameError: name 'messagebox' is not defined

If I add to the import line an explicit import for messagebox:

from tkinter import *
from tkinter import messagebox

it works, but I don't understand the reason why I have to add this import.

Answer 1

messagebox is a module , eg messagebox.py . This is not automatically imported into the namespace when you from tkinter import * . What is automatically imported is what tkinter.__init__ defines as __all__ :

__all__ = [name for name, obj in globals().items()
           if not name.startswith('_') and not isinstance(obj, types.ModuleType)
           and name not in {'wantobjects'}]

Notice that tkinter even explicitly excludes anything that is types.ModuleType , which messagebox falls under.

When in doubt about this type of thing, you can always check out the CPython tkinter Python lib itself .

The Python docs' Importing * From a Package contain more detail.