fixed for cases where just a tuple is fed to sort_by

Author: jaymedina

astroquery/mast/services.py

@@ -285,6 +285,10 @@ def service_request_async(self, service, params, page_size=None, page=None, use_
         # was specified
         if 'sort_by' in params.keys():
             new_sort_by = []
+
+            # If just a tuple is fed, turn it into a list with a single tuple element
+            if not isinstance(params['sort_by'], list):
+                params['sort_by'] = [(params['sort_by'][0], params['sort_by'][1])]
             for item in params['sort_by']:
                 if item[0].lower() in ['asc', 'desc']:
                     new_sort_by.append(item[1] + '.' + item[0])
@@ -324,17 +328,9 @@ def _build_catalogs_params(self, params):
             elif prop == 'page_size':
                 catalog_params.extend(('pagesize', value))
             elif prop == 'sort_by':
-                # Loop through each value if list
-                if isinstance(value, list):
-                    for sort_item in value:
-                        catalog_params.append(('sort_by', sort_item))
-                else:
-                    # A single sort
-                    # Determine if tuple with sort direction
-                    if isinstance(value, tuple):
-                        catalog_params.append(('sort_by', value[0] + '.' + value[1]))
-                    else:
-                        catalog_params.append(('sort_by', value))
+                # Loop through each value
+                for sort_item in value:
+                    catalog_params.append(('sort_by', sort_item))
             elif prop == 'columns':
                 catalog_params.extend(tuple(('columns', col) for col in value))
             else: