Use custom error class for email change failures

judge/views/user.py

@@ -576,6 +576,9 @@ def post(self, request, *args, **kwargs):
 
 
 class EmailChangeActivateView(LoginRequiredMixin, View):
+    class EmailChangeFailedError(Exception):
+        pass
+
     def get(self, request, *args, **kwargs):
         activation_key = kwargs['activation_key']
         signer = signing.TimestampSigner()
@@ -586,22 +589,24 @@ def get(self, request, *args, **kwargs):
                     max_age=settings.DMOJ_EMAIL_CHANGE_EXPIRY_MINUTES * 60,
                 )
             except (binascii.Error, signing.BadSignature):
-                raise ValueError(_('Invalid activation key. Please try again.'))
+                raise self.EmailChangeFailedError(_('Invalid activation key. Please try again.'))
             except signing.SignatureExpired:
-                raise ValueError(_('This request has expired. Please try again.'))
+                raise self.EmailChangeFailedError(_('This request has expired. Please try again.'))
             if data['id'] != request.user.id:
-                raise ValueError(
+                raise self.EmailChangeFailedError(
                     _('Please try again from the account this email change was originally requested from.'),
                 )
             with revisions.create_revision(atomic=True):
                 if User.objects.filter(email=data['email']).exists():
-                    raise ValueError(_('The email originally requested is in use. Please try again with a new email.'))
+                    raise EmailChangeFailedError(
+                        _('The email originally requested is in use. Please try again with a new email.'),
+                    )
                 request.user.email = data['email']
                 request.user.save()
                 revisions.set_user(request.user)
                 revisions.set_comment(_('Changed email address'))
-        except ValueError as ve:
-            return generic_message(request, _('Email change failed'), str(ve), status=403)
+        except self.EmailChangeFailedError as e:
+            return generic_message(request, _('Email change failed'), str(e), status=403)
         else:
             return generic_message(
                 request,