Introduce pyupgrade

Closes #1742 (closed)

Introducing pyupgrade.

Again, I've made one commit per rule.

arkindex/images/models.py

@@ -156,11 +156,11 @@ class ImageServer(models.Model):
         folder_slash = folder.lstrip("/") + "/"
         images = self.images.filter(path__startswith=folder_slash)
         if not images.exists():
-            raise ValueError('No images are in the "{}" folder'.format(folder))
+            raise ValueError(f'No images are in the "{folder}" folder')
 
         # Create the new server on the subfolder
         new_server = ImageServer.objects.create(
-            display_name="{}_{}".format(self.display_name, slugify(folder)),
+            display_name=f"{self.display_name}_{slugify(folder)}",
             url=urllib.parse.urljoin(self.url.lstrip("/") + "/", folder),
         )
 
@@ -218,8 +218,8 @@ class Image(S3FileMixin, IndexableModel):
         if max_width is None and max_height is None:
             resize = "full"
         else:
-            resize = "{0},{1}".format(max_width or "", max_height or "")
-        return "{0}/full/{1}/0/default.jpg".format(self.url.rstrip("/"), resize)
+            resize = "{},{}".format(max_width or "", max_height or "")
+        return "{}/full/{}/0/default.jpg".format(self.url.rstrip("/"), resize)
 
     @property
     def s3_put_url(self):
@@ -359,7 +359,7 @@ class Thumbnail(S3FileMixin):
 
     @property
     def name(self):
-        return "{}.jpg".format(str(self.element.id.hex))
+        return f"{str(self.element.id.hex)}.jpg"
 
     @cached_property
     def s3_key(self):