`_pyio.BytesIO.peek()` returns bytearray instead of bytes

[fedonman]

Bug description:

_pyio.BytesIO.peek() returns a bytearray, while io.BytesIO.peek() returns bytes, which is what Doc/library/io.rst documents. It also rejects an __index__-able size that the C version accepts.

import io, _pyio

class Idx:
    def __index__(self):
        return 3

for mod in (io, _pyio):
    b = mod.BytesIO(b'abcdef')
    print(mod.__name__, 'peek()      ->', type(b.peek()).__name__)
    print(mod.__name__, 'peek(Idx()) ->', repr(b.peek(Idx())))

io peek()      -> bytes
io peek(Idx()) -> b'abc'
_pyio peek()      -> bytearray
_pyio peek(Idx()) -> TypeError: '<' not supported between instances of 'Idx' and 'int'

BytesIO.peek() is new in 3.16 (GH-150917).

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-155389: Return bytes from _pyio.BytesIO.peek() #155390