How Django Processes Model Classes part 4.1 | Python is Django

one of Django’s most recognizable features is its declarative syntax for model definitions.
With this, model definitions can be simple and concise, while still providing a vast array of functionality.
The basic process of using metaclasses for declarative syntax is described in detail in previous parts , but there are more specific steps taken
when handling models, which deserve some extra attention.
The metaclass responsible for processing model definitions is ModelBase, living at django.db.models.base.
This provides a few key features, listed here in the order in which the actions are performed.

1. A new class is generated to be used for the actual model, preserving the module location
where the original model was defined.
2. If a custom app_label wasn’t provided for the model, it’s determined based on the module
where it was declared.
3. Meta options are pulled out of the model and placed in a special Options object, which is
described in more detail later in this tutorial.
4. Two special exception classes, DoesNotExist and MultipleObjectsReturned, are created
and customized for the new model.
5. A default manager is assigned to the model if one wasn’t already provided.
6. If the model was already defined—which can happen because of differences in how
the module was imported at different stages—the existing model is retrieved from the
application cache and returned, making sure that the same class object is always used.
7. Attributes and methods defined on the original model are added to the newly-created
model class.
8. Settings from inherited parent models are set on the new model.
9. The new model is registered with the application cache for future reference.
10. The newly-created model is returned to be used in place of the class that was defined in
the source file.