feature: Torch dependency in sagameker-core to be made optional (5457)

sagemaker-core/pyproject.toml

@@ -32,7 +32,6 @@ dependencies = [
     "smdebug_rulesconfig>=1.0.1",
     "schema>=0.7.5",
     "omegaconf>=2.1.0",
-    "torch>=1.9.0",
     "scipy>=1.5.0",
     # Remote function dependencies
     "cloudpickle>=2.0.0",
@@ -57,10 +56,17 @@ codegen = [
     "pytest>=8.0.0, <9.0.0",
     "pylint>=3.0.0, <4.0.0"
 ]
+torch = [
+    "torch>=1.9.0",
+]
+all = [
+    "torch>=1.9.0",
+]
 test = [
     "pytest>=8.0.0, <9.0.0",
     "pytest-cov>=4.0.0",
     "pytest-xdist>=3.0.0",
+    "torch>=1.9.0",
 ]
 
 [project.urls]

sagemaker-core/src/sagemaker/core/deserializers/base.py

@@ -366,7 +366,10 @@ def __init__(self, accept="tensor/pt"):
 
             self.convert_npy_to_tensor = from_numpy
         except ImportError:
-            raise Exception("Unable to import pytorch.")
+            raise ImportError(
+                "Unable to import torch. Please install torch to use TorchTensorDeserializer: "
+                "pip install 'sagemaker-core[torch]'"
+            )
 
     def deserialize(self, stream, content_type="tensor/pt"):
         """Deserialize streamed data to TorchTensor

sagemaker-core/src/sagemaker/core/serializers/base.py

@@ -443,7 +443,13 @@ class TorchTensorSerializer(SimpleBaseSerializer):
 
     def __init__(self, content_type="tensor/pt"):
         super(TorchTensorSerializer, self).__init__(content_type=content_type)
-        from torch import Tensor
+        try:
+            from torch import Tensor
+        except ImportError:
+            raise ImportError(
+                "Unable to import torch. Please install torch to use TorchTensorSerializer: "
+                "pip install 'sagemaker-core[torch]'"
+            )
 
         self.torch_tensor = Tensor
         self.numpy_serializer = NumpySerializer()

sagemaker-core/tests/unit/test_torch_optional_dependency.py

@@ -0,0 +1,105 @@
+# Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"). You
+# may not use this file except in compliance with the License. A copy of
+# the License is located at
+#
+#     http://aws.amazon.com/apache2.0/
+#
+# or in the "license" file accompanying this file. This file is
+# distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
+# ANY KIND, either express or implied. See the License for the specific
+# language governing permissions and limitations under the License.
+"""Tests for torch optional dependency behavior."""
+from __future__ import absolute_import
+
+import sys
+from unittest.mock import patch, MagicMock
+
+import numpy as np
+import pytest
+
+
+def test_torch_tensor_serializer_raises_import_error_when_torch_missing():
+    """Verify TorchTensorSerializer raises ImportError with helpful message when torch is missing."""
+    import importlib
+    import sagemaker.core.serializers.base as base_module
+
+    with patch.dict(sys.modules, {"torch": None}):
+        # Reload to clear any cached imports
+        importlib.reload(base_module)
+        with pytest.raises(ImportError, match="pip install 'sagemaker-core\\[torch\\]'"):
+            base_module.TorchTensorSerializer()
+
+    # Reload again to restore normal state
+    importlib.reload(base_module)
+
+
+def test_torch_tensor_deserializer_raises_import_error_when_torch_missing():
+    """Verify TorchTensorDeserializer raises ImportError with helpful message when torch is missing."""
+    import importlib
+    import sagemaker.core.deserializers.base as base_module
+
+    with patch.dict(sys.modules, {"torch": None}):
+        importlib.reload(base_module)
+        with pytest.raises(ImportError, match="pip install 'sagemaker-core\\[torch\\]'"):
+            base_module.TorchTensorDeserializer()
+
+    # Reload again to restore normal state
+    importlib.reload(base_module)
+
+
+def test_torch_tensor_serializer_works_when_torch_installed():
+    """Verify TorchTensorSerializer can be instantiated when torch is available."""
+    from sagemaker.core.serializers.base import TorchTensorSerializer
+
+    serializer = TorchTensorSerializer()
+    assert serializer is not None
+    assert serializer.CONTENT_TYPE == "tensor/pt"
+
+
+def test_torch_tensor_deserializer_works_when_torch_installed():
+    """Verify TorchTensorDeserializer can be instantiated when torch is available."""
+    from sagemaker.core.deserializers.base import TorchTensorDeserializer
+
+    deserializer = TorchTensorDeserializer()
+    assert deserializer is not None
+    assert deserializer.ACCEPT == ("tensor/pt",)
+
+
+def test_sagemaker_core_imports_without_torch():
+    """Verify that importing serializers/deserializers modules does not fail without torch."""
+    import importlib
+    import sagemaker.core.serializers.base as ser_base
+    import sagemaker.core.deserializers.base as deser_base
+
+    with patch.dict(sys.modules, {"torch": None}):
+        # Reloading the modules should not raise since torch imports are lazy (in __init__)
+        importlib.reload(ser_base)
+        importlib.reload(deser_base)
+
+    # Restore
+    importlib.reload(ser_base)
+    importlib.reload(deser_base)
+
+
+def test_other_serializers_work_without_torch():
+    """Verify non-torch serializers work normally even if torch is unavailable."""
+    import importlib
+    import sagemaker.core.serializers.base as base_module
+
+    with patch.dict(sys.modules, {"torch": None}):
+        importlib.reload(base_module)
+
+        csv_ser = base_module.CSVSerializer()
+        assert csv_ser.serialize([1, 2, 3]) == "1,2,3"
+
+        json_ser = base_module.JSONSerializer()
+        assert json_ser.serialize([1, 2, 3]) == "[1, 2, 3]"
+
+        numpy_ser = base_module.NumpySerializer()
+        result = numpy_ser.serialize(np.array([1, 2, 3]))
+        assert result is not None
+
+    # Restore
+    importlib.reload(base_module)