Django signals not working when placed outside models.py

Question

I'm trying to print some text after Django model in an app has been saved.

I have created a signal for that in a signals.py file in the same application.

However, it's not working as expected (i.e., the function is not being called and text is not being printed)

But if I place the receiver function in the models.py file just below the model that I created, it's working fine (i.e., the function is being called and text has been printed)

I have gone through the documentation to check if there is any need to place the signals in a specific file or location. It looks like there isn't any such restriction.

https://docs.djangoproject.com/en/3.0/topics/signals/#django.dispatch.receiver

Why is this behaving differently if there is no such restriction?

signals.py:

from django.db.models.signals import post_save
from django.dispatch import receiver
from aws_envs.models import UserStack

@receiver(post_save, sender=UserStack)
def create_user_stack(sender, **kwargs):
    print("creating user stack now")

models.py:

class UserStack(BaseModel):

    name = models.CharField(max_length=50)
    email = models.EmailField(unique=True, max_length=50, blank=False)
    enabled = models.BooleanField(default=True)

    def save(self, *args, **kwargs):
        print(f"Creating stack with data: {self.name, self.email}")
        super(UserStack, self).save(*args, **kwargs)

    def __str__(self):
        return self.name, self.email

Answer 1

1. in INSTALLED_APPS you should register like this:

'post.apps.PostConfig'

I.e. in settings.py replace

INSTALLED_APPS = (
 '...',
 'post,
)

with

INSTALLED_APPS = (
 '...',
 'post.apps.PostConfig',
)

2. in apps.py you shoud add these:

from django.apps import AppConfig

class postConfig(AppConfig):
    name = 'post'

    def ready(self):
        # signals are imported, so that they are defined and can be used
        import post.signals

3. created a file in app's folder

# post/signals.py
from django.dispatch import receiver
from django.db.models.signals import post_save
from post.models import Post

def send():
    print("send email!")

@receiver(post_save, sender=Post, dispatch_uid='Post_post_save')
def send_email(instance, **kwargs):
    send()