QUERY · ISSUE

bytearray slice assignment fails for derived types

openby mbueschopened 2015-12-11updated 2024-08-28

docs

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

CANDIDATE · ISSUE

bytesarray buffer manipulation/copy fail

closedby nedoskivopened 2019-05-23updated 2019-05-23

Hello,

I'm not a big expert at this, so I googled a little and found this topic:

https://stackoverflow.com/questions/10633881/how-to-copy-a-python-bytearray-buffer

but it do not work for me:

`c=b'\x11\x11'

a=b'\xff\xff'
a[:]=c
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'bytes' object doesn't support item assignment`

Also tried to change in lots of way value of any byte in the array it returns same error. Did I do something wrong or there is something not yet implemented?

Assessment

Q Qwen · medium

Both issues involve bytearray slice assignment problems, but they describe different root causes and symptoms. Issue #1710 is about bytearray subclasses being incorrectly rejected during slice assignment (type checking too strict). Issue #4810 is about assigning bytes to a bytearray slice, which fails because bytes objects are immutable and don't support item assignment - this is a fundamental type mismatch, not a subclass/type-checking issue. The error signatures differ ('NotImplementedError: array/bytes required' vs 'TypeError: bytes object doesn't support item assignment'). While both touch bytearray.setitem, they address different problems.

Suggested action

Keep both issues open as they address different bugs. #1710 needs a fix for type checking in slice assignment to allow bytearray subclasses, while #4810 is a user error (trying to assign immutable bytes to mutable bytearray slice) or may need better error messaging.

bytearray slice assignment fails for derived types

bytesarray buffer manipulation/copy fail

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