如何只导入__init__.py的一部分？

Question

I have a package with some files and I'm having some importation issues. Let's say I have the following files:

main.py
Lib
 ├─ __init__.py
 ├─ file1.py
 └─ file2.py

main.py :

from Lib import ClassA

foo = ClassA('anything')

Lib/init.py :

from .file1 import ClassA
from .file2 import ClassB

file1.py :

import a_lot_of_things

class ClassA:
  pass

file2.py :

import a_lot_of_other_things

class ClassB:
  pass

This code works, but Python will also import all the other classes in the file, as the ClassB. The problem is that Python takes a lot of time importing all the libraries of file2.py which I don't wanna use.

I know it happens because Python is running init.py and it is importing all classes, even if I ask for just one. But I think it should do this only if I write:

from Lib import *

Is there a way to, inside init.py, check if I'm importing all or just one specific class to run just this file/importation?

I also tried to structure my directory this way:

main.py
Lib
 ├─ __init__.py
 ├─ ClassA
 │   ├─ __init__.py
 │   └─ file1.py
 └─ ClassB 
     ├─ __init__.py
     └─ file2.py

So I cleaned Lib/init.py and put the importations into each init.py.

ClassA/init.py :

from .file1 import ClassA

ClassB/init.py :

from .file2 import ClassB

But now I need to use it this way:

main.py :

from Lib import ClassA

foo = ClassA.ClassA('anything')

And I'd like to use it directly, as I wrote before. Is there a way to do this?

Answer 1

If you import a module (or import something from within a module) everything that that module imports will also be imported.

You can only avoid this by placing imports within a local context

For example

my_module:

import some_stuff

def do_stuff()
    pass

def do_some_specific_things()
    import some_specific_stuff_only_relevant_to_this_function
    pass

If you now call from my_module import do_stuff then import some_stuff will be executed, but import some_specific_stuff_only_relevant_to_this_function will not.

By the way, structuring your code as follows does not make sense:

main.py
Lib
 ├─ __init__.py
 ├─ ClassA
 │   ├─ __init__.py
 │   └─ file1.py
 └─ ClassB 
     ├─ __init__.py
     └─ file2.py

A class is within a module( file1 and file2 are modules). A module cannot sit within a class.