Cannot convert list to array: ValueError: only one element tensors can be converted to Python scalars

It seems like you have a list of tensors. For each tensor you can see its size() (no need to convert to list/numpy). If you insist, you can convert a tensor to numpy array using numpy():

Return a list of tensor shapes:

>> [t.size() for t in my_list_of_tensors]

Returns a list of numpy arrays:

>> [t.numpy() for t in my_list_of_tensors]

In terms of performance, it is always best to avoid casting of tensors into numpy arrays, as it may incur sync of device/host memory. If you only need to check the shape of a tensor, use size() function.