Backports for v0.14.2 (#3063)

* Fix `iterable.Cached`. (#3060)

* Torch: Remove double caching of dataset. (#3061)

---------

Co-authored-by: Jasper <schjaspe@amazon.de>

Author: lostella

src/gluonts/itertools.py

@@ -305,10 +305,9 @@ def split_into(xs: Sequence, n: int) -> Sequence:
 @dataclass
 class Cached:
     """
-    An iterable wrapper, which caches values in a list the first time it is
-    iterated.
+    An iterable wrapper, which caches values in a list while iterated.
 
-    The primary use-case for this is to avoid re-computing the element of the
+    The primary use-case for this is to avoid re-computing the elements of the
     sequence, in case the inner iterable does it on demand.
 
     This should be used to wrap deterministic iterables, i.e. iterables where
@@ -317,15 +316,21 @@ class Cached:
     """
 
     iterable: SizedIterable
-    cache: list = field(default_factory=list, init=False)
+    provider: Iterable = field(init=False)
+    consumed: list = field(default_factory=list, init=False)
+
+    def __post_init__(self):
+        # ensure we only iterate once over the iterable
+        self.provider = iter(self.iterable)
 
     def __iter__(self):
-        if not self.cache:
-            for element in self.iterable:
-                yield element
-                self.cache.append(element)
-        else:
-            yield from self.cache
+        # Yield already provided values first
+        yield from self.consumed
+
+        # Now yield remaining elements.
+        for element in self.provider:
+            self.consumed.append(element)
+            yield element
 
     def __len__(self) -> int:
         return len(self.iterable)

src/gluonts/torch/model/estimator.py

@@ -11,7 +11,7 @@
 # express or implied. See the License for the specific language governing
 # permissions and limitations under the License.
 
-from typing import NamedTuple, Optional, Iterable, Dict, Any, Union
+from typing import NamedTuple, Optional, Iterable, Dict, Any
 import logging
 
 import numpy as np
@@ -24,7 +24,7 @@
 from gluonts.itertools import Cached
 from gluonts.model import Estimator, Predictor
 from gluonts.torch.model.predictor import PyTorchPredictor
-from gluonts.transform import Transformation, TransformedDataset
+from gluonts.transform import Transformation
 
 logger = logging.getLogger(__name__)
 
@@ -156,18 +156,16 @@ def train_model(
         transformation = self.create_transformation()
 
         with env._let(max_idle_transforms=max(len(training_data), 100)):
-            transformed_training_data: Union[
-                Cached, TransformedDataset
-            ] = transformation.apply(training_data, is_train=True)
+            transformed_training_data: Dataset = transformation.apply(
+                training_data, is_train=True
+            )
             if cache_data:
                 transformed_training_data = Cached(transformed_training_data)
 
             training_network = self.create_lightning_module()
 
             training_data_loader = self.create_training_data_loader(
-                Cached(transformed_training_data)
-                if cache_data
-                else transformed_training_data,
+                transformed_training_data,
                 training_network,
                 shuffle_buffer_length=shuffle_buffer_length,
             )
@@ -176,9 +174,9 @@ def train_model(
 
         if validation_data is not None:
             with env._let(max_idle_transforms=max(len(validation_data), 100)):
-                transformed_validation_data: Union[
-                    Cached, TransformedDataset
-                ] = transformation.apply(validation_data, is_train=True)
+                transformed_validation_data: Dataset = transformation.apply(
+                    validation_data, is_train=True
+                )
                 if cache_data:
                     transformed_validation_data = Cached(
                         transformed_validation_data

test/test_itertools.py

@@ -119,6 +119,16 @@ def test_pickle(iterable: Iterable, assert_content: bool):
         assert data == data_copy
 
 
+def test_cached_reentry():
+    data = Cached(range(10))
+
+    assert len(data) == 10
+    assert list(take(5, data)) == list(range(5))
+    assert len(data) == 10
+    assert list(take(10, data)) == list(range(10))
+    assert len(data) == 10
+
+
 @pytest.mark.parametrize(
     "given, expected",
     [