Update app.py

app.py

@@ -304,7 +304,7 @@ class BM25Index(InvertedIndex):
 
     @classmethod
     def build_from_documents(
-        cls: Type[BM25Index],
+        cls: Type["BM25Index"],
         documents: Iterable[Document],
         store_raw: bool = True,
         output_dir: Optional[str] = None,
@@ -312,7 +312,7 @@ class BM25Index(InvertedIndex):
         show_progress_bar: bool = True,
         k1: float = 0.9,
         b: float = 0.4,
-    ) -> BM25Index:
+    ) -> "BM25Index":
         # Counting TFs, DFs, doc_lengths, etc.:
         counting = run_counting(
             documents=documents,
@@ -428,7 +428,7 @@ class CSCBM25Index(CSCInvertedIndex):
 
     @classmethod
     def build_from_documents(
-        cls: Type[CSCBM25Index],
+        cls: Type["CSCBM25Index"],
         documents: Iterable[Document],
         store_raw: bool = True,
         output_dir: Optional[str] = None,
@@ -436,7 +436,7 @@ class CSCBM25Index(CSCInvertedIndex):
         show_progress_bar: bool = True,
         k1: float = 0.9,
         b: float = 0.4,
-    ) -> CSCBM25Index:
+    ) -> "CSCBM25Index":
         # Counting TFs, DFs, doc_lengths, etc.:
         counting = run_counting(
             documents=documents,