This is one of most annoying things in Python to me. When you want accept any bytes-like object in you bytes-processing function you need special case empty input. def foo(data): data = memoryview(data) if data: data = data.cast('B') else: data = b'' You can't use just memoryview(data).cast('B') because it doesn't work for empty data. >>> memoryview(b'').cast('b') Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: memoryview: cannot cast view with zeros in shape or strides It would be very nice to allow cast() for empty views.

This actually sounds like a bug to me. A view over the empty bytestring is a one-dimensional zero-length view, it isn't a special kind of entity.

Cool. Therefore I can hope on fixing this in maintained releases?

> Cool. Therefore I can hope on fixing this in maintained releases? Provided someone makes a patch :-)

Here is a patch. I can't tell whether it's right for sure, since the whole buffer thing has become so complicated.

I agree that this cast should work. Perhaps disallowing zero strides is enough -- I have to look at this more closely though.

Ok, I think the main reason for disallowing zeros in view->shape here was that casts are undefined if also the "shape" argument is given: x = memoryview(b'') x.cast('d', shape=[1]) Now, this case *is* already caught at a later stage, since there isn't enough space for the cast. Nevertheless, the code is tricky, so I'd prefer to be conservative and catch shape arguments earlier. I left a suggestion in Rietveld. I would commit it myself, but I'm moving and my infrastructure is a mess. It would be great if one of you could take this one. I'll try to review the general case for ndim > 1 later, but that's not particularly important right now.

New changeset b08e092df155 by Antoine Pitrou in branch '3.3': Issue #19014: memoryview.cast() is now allowed on zero-length views. http://hg.python.org/cpython/rev/b08e092df155 New changeset 1e13a58c1b92 by Antoine Pitrou in branch 'default': Issue #19014: memoryview.cast() is now allowed on zero-length views. http://hg.python.org/cpython/rev/1e13a58c1b92

Applied Stefan's suggestion. Thanks for the review :)

Thank you Antoine.