OK, here's the new patch. I added tests for array(typecode, bytearray(b'abab')), a.extend(b'123') and a.extend(bytearray(b'123')). 

@Victor: int itemsize is the array's item size, buffer.itemsize is the strings' (and must be 1)

PROBLEM with this patch:

I changed "s#" to "y*". This means that str arguments are no longer accepted by fromstring. I don't think they ever should have been in 3.x, but it is an incompatible change and this got the test suite, which (I assume the code hasn't changed since 2.x) used a str argument. (changed in patch). It might be best to use "s*" instead of "y*", especially if this is applied to 3.1?