Fix CNNDM dataset tests (#2246)

Author: NicolasHug

torchtext/datasets/cnndm.py

@@ -77,12 +77,21 @@ def _hash_urls(s: tuple):
 
 
 def _get_split_list(source: str, split: str):
+    from torchdata.datapipes.iter import (  # noqa
+        IterableWrapper,
+        OnlineReader,
+    )
     url_dp = IterableWrapper([SPLIT_LIST[source + "_" + split]])
     online_dp = OnlineReader(url_dp)
     return online_dp.readlines().map(fn=_hash_urls)
 
 
 def _load_stories(root: str, source: str, split: str):
+    from torchdata.datapipes.iter import (  # noqa
+        FileOpener,
+        IterableWrapper,
+        GDriveReader,
+    )
     split_list = set(_get_split_list(source, split))
     story_dp = IterableWrapper([URL[source]])
     cache_compressed_dp = story_dp.on_disk_cache(
@@ -135,12 +144,6 @@ def CNNDM(root: str, split: Union[Tuple[str], str]):
         raise ModuleNotFoundError(
             "Package `torchdata` not found. Please install following instructions at https://github.com/pytorch/data"
         )
-    from torchdata.datapipes.iter import (  # noqa
-        FileOpener,
-        IterableWrapper,
-        OnlineReader,
-        GDriveReader,
-    )
 
     cnn_dp = _load_stories(root, "cnn", split)
     dailymail_dp = _load_stories(root, "dailymail", split)