Python Type Hinting : Eliminating ImportError Due to Circular Imports

Muminur Rahman — Sat, 31 Jul 2021 06:01:20 +0000

We all face sometimes ImportError due to having a circular import that is occurred only for type hinting. There is a simple way to handle this kind of problem.
Let’s take we have two files like following:

#book_manager.py
from django.db import models

class BookManager(models.Manager):
    def create_new_version_of_book(self, old_book_object, version):
        return self.create(name=old_book_object.name, version=version)

The another file:

from django.db import models

from library.models import BookManager

class Book(models.Model):
    name = models.CharField(max_length=200)
    version = models.CharField(max_length=50)

    objects = BookManager()

These two files will work fine as we did not added any type hinting. Only the BookManager is imported in book_model.py file. But if we add type hint to the create_new_version_of_book method from BookManager, then it will be as follows:

from django.db import models

from library.models import Book


class BookManager(models.Manager):

    def create_new_version_of_book(self, old_book_object: Book, version: str) -> Book:
        return self.create(name=old_book_object.name, version=version)

Here now we will get an ImportError due to circular import and we will get something like the below message when we want to run the project/files:

ImportError: cannot import name 'BookManager' from partially initialized module 'library.models' (most likely due to a circular import)

The solution is using typing.TYPE_CHECKING constant as below:

from __future__ import annotations

from typing import TYPE_CHECKING

from django.db import models

if TYPE_CHECKING:
    from library.models import Book


class BookManager(models.Manager):

    def create_new_version_of_book(self, old_book_object: Book, version: str) -> Book:
        return self.create(name=old_book_object.name, version=version)

Line 1: We have imported annotations. __future__.annotations is not default in Python now; but it will become the default in Python 3.11. For details, you have a look into PEP 563. If you don’t import it, you can use type hints as string. In our case, it will be old_book_object: ‘Book’.

Line 3: We have imported typing.TYPE_CHECKING special constant. The value of the constant is always False, but set to True by any type checkers, such as Mypy. We have used the this constant to make our import conditional.

Line 7–8: We have imported the model with a condition, so it will only be imported when the TYPE_CHECKING variable is True.

Hope, this will help. :)

How To Integrate CKEditor with Django Admin

Muminur Rahman — Mon, 24 Feb 2020 17:27:37 +0000

Sometimes we have to add WYSIWYG editor to an input box in the Django Admin. It is a simple and easy task but may seem tricky for newbies. So, we are going to add a WYSIWYG (which s an acronym for “What You See Is What You Get”) editor to our Django Admin.
For this tutorial, I am assuming that we have a ProjectUpdate model where we need to integrate a WYSIWYG editor. I am using CKEditor 5 for this tutorial.

Add an id to Admin Textarea

At first, we need to add id to the textarea in Django Admin so that we can find it through the id and bind it with CKEditor. For that, we will use formfield_overrides that provides a quick-and-dirty way to override some of the field options on Django admin.
# myproject/admin.py class ProjectUpdateAdmin(admin.ModelAdmin): formfield_overrides = { models.TextField: {'widget': Textarea( attrs={'id': 'project_update_textarea'})} }
Here we have added an id project_update_textarea to every textfield in Django admin panel of the ProjectUpdate model.

Add the script to base.html

At first, make a directory named admin in your templates directory and copy the base.html file there. The admin base template can be found in this path: django/contrib/admin/templates/admin/base.html. After that, add these lines before the body closing tag:
# templates/admin/base.httemplates/admin/base.httemplates/admin/base.html  <script src="{% static 'vendor/ckeditor5/ckeditor.js' %}"></script> <script> ClassicEditor .create( document.querySelector( '#project_update_textarea' ) ) .catch( error => { console.error( error ); } ); </script> 
I have downloaded the CKEditor package and stored in static/vendor/ckeditor5 directory. Hence, I have used the static tag in the script. You can use the CDN link also if you prefer.

Conclusion

That’s it. Go to your Django Admin Panel. The CKEditor should work now.

DEV Community: Muminur Rahman

Python Type Hinting : Eliminating ImportError Due to Circular Imports

How To Integrate CKEditor with Django Admin

Add an id to Admin Textarea

Add the script to base.html

Conclusion