Warns on read-only Numpy array->tensor conversion (#33615)
Summary:
Addresses https://github.com/pytorch/pytorch/issues/5442.
Per title (and see issue). A test is added to test_torch.py to verify the behavior.
Update (with new behavior):
NumPy arrays can be non-writeable (read-only). When converting a NumPy array to a Torch tensor the storage is shared, but the tensor is always writable (PyTorch doesn't have a read-only tensor). Thus, when a non-writeable NumPy array is converted to a PyTorch tensor it can be written to.
In the past, PyTorch would silently copy non-writeable NumPy arrays and then convert those copies into tensors. This behavior violates the from_numpy contract, however, which promises that the tensor and the array share memory.
This PR adds a warning message when a non-writeable NumPy array is converted into a Torch tensor. This will not break any networks, but will make end users aware of the behavior. They can work-around the warning message by marking their NumPy arrays as writeable.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33615
Differential Revision: D20289894
Pulled By: mruberry
fbshipit-source-id: b76df0077399eb91038b12a6bf1917ef38c2cafd
