Fix TextSplitter.from_tiktoken(langchain-ai#4361)

Thanks to @danb27 for the fix! Minor update

Fixes langchain-ai#4357

---------

Co-authored-by: Dan Bianchini <42096328+danb27@users.noreply.github.com>

langchain/text_splitter.py

@@ -14,6 +14,8 @@
     Literal,
     Optional,
     Sequence,
+    Type,
+    TypeVar,
     Union,
 )
 
@@ -22,6 +24,8 @@
 
 logger = logging.getLogger(__name__)
 
+TS = TypeVar("TS", bound="TextSplitter")
+
 
 class TextSplitter(BaseDocumentTransformer, ABC):
     """Interface for splitting text into chunks."""
@@ -139,13 +143,13 @@ def _huggingface_tokenizer_length(text: str) -> int:
 
     @classmethod
     def from_tiktoken_encoder(
-        cls,
+        cls: Type[TS],
         encoding_name: str = "gpt2",
         model_name: Optional[str] = None,
         allowed_special: Union[Literal["all"], AbstractSet[str]] = set(),
         disallowed_special: Union[Literal["all"], Collection[str]] = "all",
         **kwargs: Any,
-    ) -> TextSplitter:
+    ) -> TS:
         """Text splitter that uses tiktoken encoder to count length."""
         try:
             import tiktoken
@@ -161,16 +165,24 @@ def from_tiktoken_encoder(
         else:
             enc = tiktoken.get_encoding(encoding_name)
 
-        def _tiktoken_encoder(text: str, **kwargs: Any) -> int:
+        def _tiktoken_encoder(text: str) -> int:
             return len(
                 enc.encode(
                     text,
                     allowed_special=allowed_special,
                     disallowed_special=disallowed_special,
-                    **kwargs,
                 )
             )
 
+        if issubclass(cls, TokenTextSplitter):
+            extra_kwargs = {
+                "encoding_name": encoding_name,
+                "model_name": model_name,
+                "allowed_special": allowed_special,
+                "disallowed_special": disallowed_special,
+            }
+            kwargs = {**kwargs, **extra_kwargs}
+
         return cls(length_function=_tiktoken_encoder, **kwargs)
 
     def transform_documents(

tests/integration_tests/test_text_splitter.py

@@ -23,19 +23,24 @@ def test_huggingface_tokenizer() -> None:
     assert output == ["foo", "bar"]
 
 
-class TestTokenTextSplitter:
-    """Test token text splitter."""
-
-    def test_basic(self) -> None:
-        """Test no overlap."""
-        splitter = TokenTextSplitter(chunk_size=5, chunk_overlap=0)
-        output = splitter.split_text("abcdef" * 5)  # 10 token string
-        expected_output = ["abcdefabcdefabc", "defabcdefabcdef"]
-        assert output == expected_output
-
-    def test_overlap(self) -> None:
-        """Test with overlap."""
-        splitter = TokenTextSplitter(chunk_size=5, chunk_overlap=1)
-        output = splitter.split_text("abcdef" * 5)  # 10 token string
-        expected_output = ["abcdefabcdefabc", "abcdefabcdefabc", "abcdef"]
-        assert output == expected_output
+def test_token_text_splitter() -> None:
+    """Test no overlap."""
+    splitter = TokenTextSplitter(chunk_size=5, chunk_overlap=0)
+    output = splitter.split_text("abcdef" * 5)  # 10 token string
+    expected_output = ["abcdefabcdefabc", "defabcdefabcdef"]
+    assert output == expected_output
+
+
+def test_token_text_splitter_overlap() -> None:
+    """Test with overlap."""
+    splitter = TokenTextSplitter(chunk_size=5, chunk_overlap=1)
+    output = splitter.split_text("abcdef" * 5)  # 10 token string
+    expected_output = ["abcdefabcdefabc", "abcdefabcdefabc", "abcdef"]
+    assert output == expected_output
+
+
+def test_token_text_splitter_from_tiktoken() -> None:
+    splitter = TokenTextSplitter.from_tiktoken_encoder(model_name="gpt-3.5-turbo")
+    expected_tokenizer = "cl100k_base"
+    actual_tokenizer = splitter._tokenizer.name
+    assert expected_tokenizer == actual_tokenizer