minor design changed to fulfill pep8

src/datastore.py

@@ -3,7 +3,6 @@ __date__ = '2019-11-22'
 
 
 from typing import Any, List, Tuple
-
 from abc import ABC
 
 
@@ -80,6 +79,13 @@ class AbstractDataStore(ABC):
         """
         pass
 
+    def list_all_names(self) -> None:
+        """
+        List all names available in the data store.
+        :return: all names
+        """
+        pass
+
 
 class DataStoreByVariable(AbstractDataStore):
 
@@ -327,5 +333,3 @@ class DataStoreByScope(AbstractDataStore):
                 if name not in names:
                     names.append(name)
         return sorted(names)
-
-