remove allow-untyped-defs for utils/data/datapipes/dataframe/structures.py (pytorch#143273)

Pull Request resolved: pytorch#143273
Approved by: https://github.com/aorenste
ghstack dependencies: pytorch#143271

Author: bobrenjc93

torch/utils/data/datapipes/dataframe/structures.py

@@ -1,4 +1,5 @@
-# mypy: allow-untyped-defs
+from typing import Any, Iterator
+
 from torch.utils.data.datapipes.dataframe import dataframe_wrapper as df_wrapper
 from torch.utils.data.datapipes.datapipe import DataChunk
 
@@ -9,11 +10,11 @@
 class DataChunkDF(DataChunk):
     """DataChunkDF iterating over individual items inside of DataFrame containers, to access DataFrames user `raw_iterator`."""
 
-    def __iter__(self):
+    def __iter__(self) -> Iterator[Any]:
         for df in self.items:
             yield from df_wrapper.iterate(df)
 
-    def __len__(self):
+    def __len__(self) -> int:
         total_len = 0
         for df in self.items:
             total_len += df_wrapper.get_len(df)