Data object allows numpy values but doesn't actually support it

[richardrl]

1. Generate a dictionary where the values are numpy arrays.
2. Load this into a Data object with Data.from_dict.

Ostensibly, we now have a valid data object. But none of the subsequent operations over this object are supported when there are numpy arrays.

For example, in line 204 of torch_geometric/data/data.py, there is a line:

item.size(...)

This will fail if item is a numpy array, and succeed if item is a torch tensor.

[rusty1s]

That is intended. All tensor data should be saved as PyTorch tensors.

[richardrl]

@rusty1s Alright, but it could be helpful to have an assertion or check for whether the input is a torch tensor. it was tricky to trace this error

[rusty1s]

You are right. I will add that in.