python – What does "from modulox import *" really mean


As far as I know this imports all classes and functions from a certain file without having to reference it in code, right? But I'm starting to think that from modulo import * doesn't mean that.

I was studying the tkinter library and I came across the following situation:

from tkinter import *
from tkinter import colorchooser

If in the first import you already used * , why would you need to import the colorchooser again? Actually apparently the colorchooser wasn't even imported.

If I try to use colorchooser without using the second line it just says it's not set. Why do you need to import colorchooser twice?


You don't matter twice. Using the asterisk does not necessarily mean that you will import all classes, functions or variables available within a module. There we have two cases…

  1. __all__ variable was not defined in file, so Python will load whatever is defined in there (which can't be the best behavior), or

  2. Import everything that is deemed necessary and that has been defined inside __all__ , which gives you much more control over what is being loaded.

For example you have a module called module and in its directory there are two files, one containing the classes, :

class Media:

class Soma:

And the other is which even indicates that this directory is a module:

__all__ = ("Media",)

from .somas import Media, Soma

In this scenario if you do:

>>> from modulo import *
>>> a = Media()
>>> b = Soma()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'Soma' is not defined

You cannot use the Soma class as only Media was automatically loaded.

It is necessary to load it manually (in this case only the Soma class):

>>> from teste import Soma
>>> b = Soma()

Or, depending on the case, by appending it inside __all__ .

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