diff --git a/pyproject.toml b/pyproject.toml
index 63c61d93..f262c10a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -117,6 +117,7 @@ files = [
 ]
 # This section is for folders with "-" as they are not valid python modules
 exclude = [
+    "src/litdata/utilities/_pytree.py",
 ]
 install_types = "True"
 non_interactive = "True"
diff --git a/src/litdata/processing/data_processor.py b/src/litdata/processing/data_processor.py
index c8a79ca9..b8b6be3d 100644
--- a/src/litdata/processing/data_processor.py
+++ b/src/litdata/processing/data_processor.py
@@ -20,7 +20,6 @@
 import signal
 import tempfile
 import traceback
-import types
 from abc import abstractmethod
 from dataclasses import dataclass
 from multiprocessing import Process, Queue
@@ -625,7 +624,7 @@ def _handle_data_chunk_recipe(self, index: int) -> None:
         try:
             current_item = self.items[index] if self.reader is None else self.reader.read(self.items[index])
             item_data_or_generator = self.data_recipe.prepare_item(current_item)
-            if isinstance(item_data_or_generator, types.GeneratorType):
+            if self.data_recipe.is_generator:
                 for item_data in item_data_or_generator:
                     if item_data is not None:
                         chunk_filepath = self.cache._add_item(self._index_counter, item_data)
diff --git a/src/litdata/processing/functions.py b/src/litdata/processing/functions.py
index 14387425..a07d7b65 100644
--- a/src/litdata/processing/functions.py
+++ b/src/litdata/processing/functions.py
@@ -130,26 +130,31 @@ def __init__(
         super().__init__(chunk_size=chunk_size, chunk_bytes=chunk_bytes, compression=compression)
         self._fn = fn
         self._inputs = inputs
+        self.is_generator = False
+
+        self.check_fn()
+
+        self.prepare_item = self._prepare_item_generator if self.is_generator else self._prepare_item  # type: ignore
+
+    def check_fn(self) -> None:
+        if (
+            isinstance(self._fn, (partial, FunctionType))
+            and inspect.isgeneratorfunction(self._fn)
+            or (callable(self._fn) and inspect.isgeneratorfunction(self._fn.__call__))  # type: ignore
+        ):
+            self.is_generator = True
+
+    def _prepare_item(self, item_metadata: Any) -> Any:
+        return self._fn(item_metadata)
+
+    def _prepare_item_generator(self, item_metadata: Any) -> Any:
+        yield from self._fn(item_metadata)  # type: ignore
 
     def prepare_structure(self, input_dir: Optional[str]) -> Any:
         return self._inputs
 
     def prepare_item(self, item_metadata: Any) -> Any:
-        if isinstance(self._fn, partial):
-            yield from self._fn(item_metadata)
-
-        elif isinstance(self._fn, FunctionType):
-            if inspect.isgeneratorfunction(self._fn):
-                yield from self._fn(item_metadata)
-            else:
-                yield self._fn(item_metadata)
-        elif callable(self._fn):
-            if inspect.isgeneratorfunction(self._fn.__call__):  # type: ignore
-                yield from self._fn.__call__(item_metadata)  # type: ignore
-            else:
-                yield self._fn.__call__(item_metadata)  # type: ignore
-        else:
-            raise ValueError(f"The provided {self._fn} isn't supported.")
+        """This method is overriden dynamically."""
 
 
 def map(
diff --git a/src/litdata/streaming/writer.py b/src/litdata/streaming/writer.py
index 21809a62..2b7aa3cb 100644
--- a/src/litdata/streaming/writer.py
+++ b/src/litdata/streaming/writer.py
@@ -142,7 +142,9 @@ def serialize(self, items: Any) -> Tuple[bytes, Optional[int]]:
         # Flatten the items provided by the users
         flattened, data_spec = tree_flatten(items)
 
-        is_single_tensor = len(flattened) == 1 and isinstance(flattened[0], torch.Tensor)
+        is_single_tensor = (
+            len(flattened) == 1 and isinstance(flattened[0], torch.Tensor) and len(flattened[0].shape) == 1
+        )
 
         # Collect the sizes and associated bytes for each item
         sizes: List[int] = []
diff --git a/status.json b/status.json
deleted file mode 100644
index 72aa5495..00000000
--- a/status.json
+++ /dev/null
@@ -1 +0,0 @@
-{ "progress": "20.0%" }
diff --git a/tests/processing/test_data_processor.py b/tests/processing/test_data_processor.py
index 2c167ccf..86cf7da8 100644
--- a/tests/processing/test_data_processor.py
+++ b/tests/processing/test_data_processor.py
@@ -362,6 +362,8 @@ def test_map_items_to_workers_sequentially(monkeypatch):
 
 
 class CustomDataChunkRecipe(DataChunkRecipe):
+    is_generator = False
+
     def prepare_structure(self, input_dir: str) -> List[Any]:
         filepaths = [os.path.join(input_dir, f) for f in os.listdir(input_dir)]
         assert len(filepaths) == 30
@@ -553,6 +555,8 @@ def test_data_processsor_distributed(fast_dev_run, delete_cached_files, tmpdir,
 
 
 class TextTokenizeRecipe(DataChunkRecipe):
+    is_generator = True
+
     def prepare_structure(self, input_dir: str) -> List[Any]:
         return [os.path.join(input_dir, "dummy.txt")]