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From: Peter Otten <__peter__@web.de>
Newsgroups: comp.lang.python
Subject: Re: submodules
Date: Fri, 18 Mar 2016 12:03:25 +0100
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Xref: csiph.com comp.lang.python:105199

ast wrote:

> Hello
> 
> Since in python3 ttk is a submodule of tkinter, I was expecting this
> to work:
> 
> from tkinter import *
> 
> root = Tk()
> nb = ttk.Notebook(root)
> 
> but it doesnt, ttk is not known.
> 
> I have to explicitely import ttk with
> 
> from tkinter import ttk
> 
> why ?

If there's no tkinter.__all__

from tkinter import *

is basically

import tkinter
globals().update(
 (name, value) for name, value in 
 vars(tkinter).items() if not name.startswith("_")
)
del tkinter

so if "from tkinter import *" doesn't inject ttk in your namespace this 
means that there is no variable tkinter.ttk. This is because there is no

from . import ttk

in tkinter/__init__.py, and automagically importing all candidate submodules 
is inefficient (and unsafe).

However, once you import tkinter.ttk the name is added

>>> import tkinter.ttk
>>> from tkinter import *
>>> ttk
<module 'tkinter.ttk' from '/usr/lib/python3.4/tkinter/ttk.py'>

so what you get with the *-import depends on what has been imported before, 
perhaps by other modules. 

Personally I'd avoid the *-import altogether...