create placeholder id once

Author: Matt Sokoloff

labelbox/schema/bulk_import_request.py

@@ -632,10 +632,11 @@ def validate_subclasses(cls, value, field):
         #Create uuid and datarow id so we don't have to define classification objects twice
         #This is caused by the fact that we require these ids for top level classifications but not for subclasses
         results = []
+        dummy_id = 'child'.center(25, '_')
         for row in value:
             results.append({
                 **row, 'dataRow': {
-                    'id': 'child'.center(25, '_')
+                    'id': dummy_id
                 },
                 'uuid': str(uuid4())
             })