Django erroneously triggers the post_save signal on instance delete - django

Question

I'm trying to send an email notification when an Article instance is created or modified. I use signals and send_mail. Everything works great while I just create and modify articles. But, if I delete an Article, I've got a notification that it was updated! This is incorrect behavior. What can be a reason (and solution)?
models.py
from django.core.mail import send_mail
from django.db.models.signals import post_save
from django.dispatch import receiver
# ...
class Article(TimeStampedModel):
title = models.CharField(_('Title'), max_length=255, db_index=True)
slug = AutoSlugField(_('Slug'), unique_with=['year', 'month'], populate_from="title", db_index=True)
picture = models.ImageField(verbose_name=_('Image'),
upload_to = upload_to)
category = models.ForeignKey('Category', blank=True, null=True,
on_delete=models.SET_NULL, db_index=True, related_name='articles')
author = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, on_delete=models.SET_NULL)
annotation = models.TextField(_('Brief annotation'), blank=True) # Brief annotation (1 paragraph)
date = models.DateTimeField(_('Date'), default=timezone.now, db_index=True)
modified = models.DateTimeField(_('Modified'), db_index=True, auto_now=True)
year = models.PositiveIntegerField(_('Year'), db_index=True, blank=True)
month = models.CharField(_('Month'), db_index=True, max_length=2, blank=True)
is_published = models.BooleanField(_('Is published'), default=False)
def delete(self, *args, **kwargs): # Remove the media files of the article together with their folder
from django.core.files.storage import default_storage
if self.picture:
with contextlib.suppress(FileNotFoundError):
default_storage.delete( self.picture_thumbnail.path )
self.picture.delete()
path = os.path.join(settings.MEDIA_ROOT, settings.CKEDITOR_UPLOAD_PATH, 'news', str(self.year), str(self.month), str(self.slug))
if os.path.isdir(path):
shutil.rmtree(path) # Remove folder
super().delete(*args, **kwargs)
def __str__(self):
# Потом допилить, чтобы год и месяц тоже выводился
return self.title # There can be other ways: year, month and slugname, for example
def get_absolute_url(self):
return reverse('news:detail', kwargs={'year': self.year, 'month': self.month, 'slug':self.slug})
class Meta:
unique_together = ("year", "month", "slug")
ordering = ['-date', '-modified',]
class Comment(models.Model):
article = models.ForeignKey(Article, on_delete=models.CASCADE, related_name='comments')
author = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, on_delete=models.SET_NULL)
text = RichTextField(_('Comment'), config_name = 'tiny')
active = models.BooleanField(_('Visible'), default=True, db_index=True)
created = models.DateTimeField(_('Created at'), auto_now_add=True, db_index=True)
updated = models.DateTimeField(_('Updated at'),auto_now=True)
def __str__(self):
return f'Comment by {self.author} on {self.article}'
class Meta:
#verbose_name_plural = _('Comments')
#verbose_name = _('Comment')
ordering = ['-created']
#receiver(post_save, sender=Article)
def email_on_article_change(sender, instance, created, **kwargs):
# if a new officer is created, compose and send the email
if created: # created -- это булевская переменная, чтобы отличать новые записи от изменений старых
action = "created"
else:
action = "updated"
title = instance.title if instance.title else "no title given"
annotation = instance.annotation if instance.annotation else "no annotation given"
author = instance.author if instance.author else 'no author assignment'
subject = 'TITLE: {0}, ANNOTATION {1}, AUTHOR: {2}'.format(title, annotation, author)
message = 'A New Article has been ' + action + '!\n'
message += 'TITLE: ' + str(title) + '\n' + 'ANNOTATION: ' + str(annotation) + '\n' + 'AUTHOR: ' + str(author) + '\n'
message += '--' * 30
send_mail(
subject,
message,
'mail#raptors.ru',
['michael_romanov#inbox.ru', 'romanov-spm#yandex.ru'],
fail_silently=False,
)
P. S. I've read on this forum that sometimes this behavior can be caused by foreign keys. My Article model has two foreign keys, author and category. Also, there is a Comment model which has a foreign key 'article'. But I can't see how they can cause this problem and how to solve it. Please help me anybody!