fix: make doc metadata keys pure strings (#38)

Signed-off-by: Panos Vagenas <[email protected]>

docling_core/transforms/metadata_extractor/simple_metadata_extractor.py

@@ -6,20 +6,18 @@
 """Simple metadata extractor module."""
 
 
-from enum import Enum
 from typing import Any
 
 from docling_core.transforms.metadata_extractor import BaseMetadataExtractor
 from docling_core.types import Document as DLDocument
 
+_DL_DOC_HASH = "dl_doc_hash"
+_ORIGIN = "origin"
+
 
 class SimpleMetadataExtractor(BaseMetadataExtractor):
     """Simple metadata extractor class."""
 
-    class _Keys(str, Enum):
-        DL_DOC_HASH = "dl_doc_hash"
-        ORIGIN = "origin"
-
     include_origin: bool = False
 
     def get_metadata(
@@ -35,10 +33,10 @@ def get_metadata(
             dict[str, Any]: the extracted metadata
         """
         meta: dict[str, Any] = {
-            self._Keys.DL_DOC_HASH: doc.file_info.document_hash,
+            _DL_DOC_HASH: doc.file_info.document_hash,
         }
         if self.include_origin:
-            meta[self._Keys.ORIGIN] = origin
+            meta[_ORIGIN] = origin
         return meta
 
     def get_excluded_embed_metadata_keys(self) -> list[str]:
@@ -47,9 +45,9 @@ def get_excluded_embed_metadata_keys(self) -> list[str]:
         Returns:
             list[str]: the metadata to exclude
         """
-        excl_keys: list[str] = [self._Keys.DL_DOC_HASH]
+        excl_keys: list[str] = [_DL_DOC_HASH]
         if self.include_origin:
-            excl_keys.append(self._Keys.ORIGIN)
+            excl_keys.append(_ORIGIN)
         return excl_keys
 
     def get_excluded_llm_metadata_keys(self) -> list[str]: