Moving this to celery.exceptions so you can import the error for inspection without raising it.

celery/exceptions.py

@@ -57,14 +57,11 @@ class MaxRetriesExceededError(Exception):
     pass
 
 
-class RetryTaskError(Exception):
-    """The task is to be retried later."""
-
-    def __init__(self, message, exc, *args, **kwargs):
-        self.exc = exc
-        Exception.__init__(self, message, exc, *args, **kwargs)
-
-
 class TaskRevokedError(Exception):
     """The task has been revoked, so no result available."""
     pass
+
+
+class NotConfigured(UserWarning):
+    """Celery has not been configured, as no config module has been found."""
+

celery/loaders/default.py

@@ -4,6 +4,7 @@ import warnings
 from importlib import import_module
 
 from celery.loaders.base import BaseLoader
+from celery.exceptions import NotConfigured
 
 DEFAULT_CONFIG_MODULE = "celeryconfig"
 
@@ -22,9 +23,6 @@ DEFAULT_UNCONFIGURED_SETTINGS = {
 }
 
 
-class NotConfigured(UserWarning):
-    """Celery has not been configured, as no config module has been found."""
-
 
 def wanted_module_item(item):
     return not item.startswith("_")