[Python] Recursion error caused by __init__ method

I have a model Folder which has a ForeignKey refering to itself in order to represent a folders structure :

class Folder(models.Model):
folder_name = models.CharField(max_length=200)
parent_folder = models.ForeignKey('self', on_delete=models.CASCADE, blank=True, null=True)

def __init__(self, *args, **kwargs):
super(Folder, self).__init__(*args, **kwargs)
if self.pk is not None:
self.initial_filepath = self.filepath()

def filepath(self):
if not self.parent_folder:
return f'media/scripts/{self.folder_name}'
else:
return f'{self.parent_folder.filepath()}/{self.folder_name}'


The issue is, when deleting a folder that has childrens in the admin panel, a recursion error occurs. I was able to determine that it was coming from the filepath method called in the __init__ one. However, what I don't understand, is why this is happening as I don't really understand how the __init__ method work.

Here's a glimpse of the unending traceback:

Traceback (most recent call last):
File "C:\Users\stephane.bernardelli\Documents\ScriptsApp\.env\lib\site-packages\django\db\models\fields\related_descriptors.py", line 187, in __get__
rel_obj = self.field.get_cached_value(instance)
File "C:\Users\stephane.bernardelli\Documents\ScriptsApp\.env\lib\site-packages\django\db\models\fields\mixins.py", line 15, in get_cached_value
return instance._state.fields_cache[cache_name]
KeyError: 'parent_folder'

During handling of the above exception, another exception occurred:

**Exact same error repeating till a recursion error occurs**


And when the recursion error occurs, I have a long message (too long for me to put it entirely) in which I found that :

File "C:\Users\stephane.bernardelli\Documents\ScriptsApp\src\scripts\models.py", line 21, in __init__
self.initial_filepath = self.filepath()
File "C:\Users\stephane.bernardelli\Documents\ScriptsApp\src\scripts\models.py", line 48, in filepath
if not self.parent_folder:
File "C:\Users\stephane.bernardelli\Documents\ScriptsApp\.env\lib\site-packages\django\db\models\fields\related_descriptors.py", line 189, in __get__
has_value = None not in self.field.get_local_related_value(instance)
File "C:\Users\stephane.bernardelli\Documents\ScriptsApp\.env\lib\site-packages\django\db\models\fields\related.py", line 742, in get_local_related_value
return self.get_instance_value_for_fields(instance, self.local_related_fields)
File "C:\Users\stephane.bernardelli\Documents\ScriptsApp\.env\lib\site-packages\django\db\models\fields\related.py", line 764, in get_instance_value_for_fields
ret.append(getattr(instance, field.attname))


admin.py

class FolderAdmin(admin.ModelAdmin):
fieldsets = [
(None, {'fields': ['folder_name']}),
('Parent Folder', {'fields': ['parent_folder']}),
]

list_display = ('folder_name', 'parent_folder')

admin.site.register(Folder, FolderAdmin)

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