Why is indexing an Anano tensor variable with a list of `slice` objects invalid?

In Dr. Goodfellow Teano's exercise tutorial, it is okay to slice x

using a tuple (slice(w,-w), )*x.ndim

, but Theano will be an exception [slice(w,-w)]*x.ndim

.

Exception information:

theano.tensor.var.AsTensorError: ('Unable to convert [slice (, Elemwise {neg, no_inplace} .0, None), slice (, Elemwise {neg, no_inplace} .0, None), slice (, Elemwise {neg, no_inplace} .0, None)] to TensorType ',)

Why isn't he working with list

? BTW, slicing a tensor variable with a whole list is fine. I blamed the document but couldn't find the reason.