Factor out dupl. code for creating list of filters

stix2/datastore/__init__.py

@@ -16,7 +16,7 @@ import uuid
 
 from six import with_metaclass
 
-from stix2.datastore.filters import Filter
+from stix2.datastore.filters import Filter, _assemble_filters
 from stix2.utils import deduplicate
 
 
@@ -312,13 +312,7 @@ class DataSource(with_metaclass(ABCMeta)):
             list: The STIX objects that matched the query.
 
         """
-        filter_list = [Filter('type', '=', obj_type)]
-        if filters:
-            if isinstance(filters, list):
-                filter_list.extend(filters)
-            else:
-                filter_list.append(filters)
-
+        filter_list = _assemble_filters(filters, [Filter('type', '=', obj_type)])
         return self.query(filter_list)
 
     def creator_of(self, obj):
@@ -421,12 +415,7 @@ class DataSource(with_metaclass(ABCMeta)):
         ids.discard(obj_id)
 
         # Assemble filters
-        filter_list = []
-        if filters:
-            if isinstance(filters, list):
-                filter_list.extend(filters)
-            else:
-                filter_list.append(filters)
+        filter_list = _assemble_filters(filters)
 
         for i in ids:
             results.extend(self.query(filter_list + [Filter('id', '=', i)]))

stix2/datastore/filters.py

@@ -44,6 +44,29 @@ def _check_filter_components(prop, op, value):
     return True
 
 
+def _assemble_filters(filter_arg, filters=[]):
+    """Assemble a list of filters.
+
+    This can be used to allow certain functions to work correctly no matter if
+    the user provides a single filter or a list of them.
+
+    Args:
+        filter_arg (Filter or list): The single Filter or list of Filters to be
+            coerced into a list of Filters.
+        filters (list, optional): A list of Filters to be automatically appended.
+
+    Returns:
+        List of Filters.
+
+    """
+    if isinstance(filter_arg, list):
+        filters.extend(filter_arg)
+    else:
+        filters.append(filter_arg)
+
+    return filters
+
+
 class Filter(collections.namedtuple("Filter", ['property', 'op', 'value'])):
     """STIX 2 filters that support the querying functionality of STIX 2
     DataStores and DataSources.