Access instance of a class - Printable Version

Access instance of a class - Printable Version

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Access instance of a class - Pavel_47 - Nov-18-2021

Hello,

In my project there is a lot of different classes, created in different .py files.
To implement some feature I need to dynamically change a property of an instance of some class.
To test how to proceed I've tried to reproduced the case in significantly simplified case.

Here is 2 files:
class_instances_test_v0.py:

import weakref

class MyClass:

    _instances = set()

    def __init__(self, name):
        self.name = name
        self._instances.add(weakref.ref(self))

    @classmethod
    def getinstances(cls):
        dead = set()
        for ref in cls._instances:
            obj = ref()
            if obj is not None:
                yield obj
            else:
                dead.add(ref)
        cls._instances -= dead

a = MyClass("a")
b = MyClass("b")
c = MyClass("c")

class_instances_test_v0_test.py:

import class_instances_test_v0.MyClass
for obj in MyClass.getinstances():
    print(obj.name)

Here is error message:
[Image: class-instances-issue.jpg]

Any comments.
Thanks.

RE: Access instance of a class - Pavel_47 - Nov-18-2021

resolved, it was typo ...
Should be ...

from class_instances_test_v0 import MyClass

Actually it's a little bit more complicated.
Due to hierarchy of files/classes I get such error (AAA and BBB names are alternate names - for ease of understanding):

Error:
ImportError: cannot import name 'AAA' from partially initialized module 'AAA.AAA' (most likely due to a circular import) ({path-to-AAA_class}/AAA/AAA.py)

In file BBB.py I use such import instruction:

form AAA.AAA import AAA

RE: Access instance of a class - Gribouillis - Nov-18-2021

Please write sensible code! What is the meaning of

from AAA.AAA import AAA

RE: Access instance of a class - Pavel_47 - Nov-18-2021

The AAA is the name related to project.
Well ... talking in different terms, it looks like this: the class AAA is defined in the file AAA.py. The file AAA.py is located in the project sub-folder AAA.

Error:
ImportError: cannot import name 'AAA' from partially initialized module 'AAA.AAA' (most likely due to a circular import) ({path-to-project-folder}/AAA/AAA.py)

RE: Access instance of a class - Pavel_47 - Nov-19-2021

Resolved:
Instead of

from AAA.AAA import AAA

use

import AAA.AAA

Then in code when the object of class AAA is referenced, use

AAA.AAA.AAA

RE: Access instance of a class - Gribouillis - Nov-19-2021

There was probably a circular import. It would be best to find it: determine which import statements are executed, in which order.
Another workaround could be

import AAA.AAA
from AAA.AAA import AAA