bytearray slice assignment fails for derived types

[mbuesch]

The type check for slice assignment to bytearray derived types seems to be a bit too strict:

class MyBytearray(bytearray): pass

a = MyBytearray(4)
b = MyBytearray(4)
a[0:4] = b

results in this error:

Traceback (most recent call last):
  File "test.py", line 5, in <module>
NotImplementedError: array/bytes required on right side

[dpgeorge]

It requires a little bit of work to support derived types on rhs of assignment.

Work around: use b[0:4] or memoryview(b) on RHS.

[pfalcon]

This issue happens not just for "derived" types, but also for "compatible", like assigning from array of different element types. So, we have "fastest path now" (effectively, a memcpy), and what we should do is to have "slowest path" - assigning from arbitrary iterable. Of course, nobody is interested to spend time on "slowest path", that's why it's not implemented ;-).

[mbuesch]

Ok, I see. I'll have to check, whether I can do a workaround in a performance neutral way, because this affects the most performance critical part of my software.

[dpgeorge]

Using a memoryview (pre created perhaps) should not impact performance at all (or very little).

[projectgus]

Labelling as docs as this has since been partially documented in 86c7507 but the description could use some elaboration.