Feature

bytes object is immutable, so constructing a new bytes object from another bytes object doesn't need copying.
However, PyBytes and PyByteArray share PyBytesInner implementation, causing an unnecessary copying of immutable data.

CPython:

>>> b = b'foo'
>>> bytes(b) is b
True

RustPython:

>>> b = b'foo'
>>> bytes(b) is b
False

Python Documentation

https://docs.python.org/3/library/stdtypes.html#bytes-objects