Importing submodule overwrites global namespace in `__init__.py`

[ChenyangGao]

Bug report

Bug description:

Assume that I have a module with the following directory structure:

./test_module
├── __init__.py
└── myfunction.py

The specific code inside the files is as follows:

__init__.py

def myfunction():
    print("myfunction")

def main():
    myfunction()

myfunction.py is an empty file.

Python 3.13.0 | packaged by Anaconda, Inc. | (main, Oct  7 2024, 16:25:56) [Clang 14.0.6 ] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from test_module import main
>>> main()
myfunction
>>> main.__globals__["myfunction"]
<function test_module.myfunction()>

Everything works fine up to this point, but when I import the myfunction module, it modifies the global namespace of the already imported __init__ module:

>>> from test_module.myfunction import *
>>> myfunction
Traceback (most recent call last):
  File "<python-input-3>", line 1, in <module>
    myfunction
NameError: name 'myfunction' is not defined
>>> main()
Traceback (most recent call last):
  File "<python-input-4>", line 1, in <module>
    main()
    ~~~~^^
  File "/Users/gcy/test_module/__init__.py", line 5, in main
    myfunction()
    ~~~~~~~~~~^^
TypeError: 'module' object is not callable
>>> main.__globals__["myfunction"]
<module 'test_module.myfunction' from '/Users/gcy/test_module/myfunction.py'>

CPython versions tested on:

3.13

Operating systems tested on:

macOS

[skirpichev]

I think this it how the import statement expected to work, i.e.: https://docs.python.org/3.13/reference/simple_stmts.html#the-import-statement

What do you expected instead and why?

[ChenyangGao]

I think this it how the import statement expected to work, i.e.: https://docs.python.org/3.13/reference/simple_stmts.html#the-import-statement

What do you expected instead and why?

I hope that if a name is already in the __init__.py, it won't be overwritten in any subsequent imports implicitly

Someone who wants to import a submodule should write it like this

import module.name as name

But if you import like this, use the name already in the __init__.py first. If that doesn't work, try loading the submodule name again

from module import name

That way, I can safely define some names in __init__.py without fear of being overwritten by the subsequent import statement and turning it into a module

That is:
- The import ... statement only loads modules
- The from ... import ... statement prioritizes the loading of existing names
- import should not overwrite an existing name unless the user obviously does so

[terryjreedy]

There is no __init__ module; test_module.__init__.py populates a module named 'test_module', just as tkinter.__init__.py populates the 'tkinter' module. There is no bug in the '>>>' interactions, which take place in the __main__ module. If you need more explanation, please ask on a help forum such as https://discuss.python.org/c/help/7. If you ask on the latter, where other beginners can see the explaination, I or someone will explain more.

[terryjreedy]

Re-reading, this is actually a feature change request which, even if technically possible (EDIT: ie, compatible with Python syntax, and I believe not), would break lots of code, making it 'socially' impossible.