How to use the catalogue.models.Style function in catalogue

def save(self, *args, **kwargs):
        update_fields=None
        clean_name = self.name.split('.')
        self.content.name = '{}_{}.{}'.format(self.record.identifier.replace(':','_'),clean_name[0],self.format.lower())
        if self.pk is not None:
            update_fields=["default","content","checksum"]
            orig = Style.objects.get(pk=self.pk)
            if orig.content:
                if orig.checksum != self._calculate_checksum(self.content):
                    if os.path.isfile(orig.content.path):
                        os.remove(orig.content.path)
                else:
                    update_fields = ["default"]
            else:
                if os.path.isfile(orig.content.path):
                    os.remove(orig.content.path)

        if update_fields:
            kwargs["update_fields"] = update_fields
        super(Style, self).save(*args, **kwargs)

from django.contrib import admin

from . import models


class CollaboratorInline(admin.StackedInline):
    model = models.Collaborator
    extra = 1
    
class StyleInline(admin.StackedInline):
    model = models.Style
    extra = 1
    
@admin.register(models.Style)
class StyleAdmin(admin.ModelAdmin):
    list_display = ('name','record','format',)
    
    def get_readonly_fields(self, request, obj=None):
        if obj:
            return self.readonly_fields + ('name',)
        return self.readonly_fields
    
    
@admin.register(models.Record)
class RecordAdmin(admin.ModelAdmin):
    list_display = ("id", "identifier", "title",)
    inlines = [StyleInline,]
    readonly_fields = ('publication_date','modified',)
    
    def get_readonly_fields(self, request, obj=None):

@receiver(pre_save, sender=Style)
def set_checksum (sender, instance, **kwargs):
    checksum = md5.new()
    checksum.update(instance.content.read())
    instance.checksum = base64.b64encode(checksum.digest())

if self.pk is not None:
            update_fields=["default","content","checksum"]
            orig = Style.objects.get(pk=self.pk)
            if orig.content:
                if orig.checksum != self._calculate_checksum(self.content):
                    if os.path.isfile(orig.content.path):
                        os.remove(orig.content.path)
                else:
                    update_fields = ["default"]
            else:
                if os.path.isfile(orig.content.path):
                    os.remove(orig.content.path)

        if update_fields:
            kwargs["update_fields"] = update_fields
        super(Style, self).save(*args, **kwargs)

def default_style(self,format):
        try:
            return self.styles.get(format=format,default=True)
        except Style.DoesNotExist:
            return None