I think there are some problems here.

1. We cannot utilize the PyBytes_Repr from Python side since bytes.__repr__ will do checks.

>>> bytes.__repr__(bytearray([1]))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: descriptor '__repr__' requires a 'bytes' object but received a 'bytearray'

2. Although PyBytes_Repr is a public API, applying it for not bytes (but supporting buffer protocol) is still weird. As it clearly states, it's a repr of bytes.

3. Using the PyObject_GetBuffer for bytes slightly hurts the performance of bytes objects.

I think 1 and 2 is the main problem here. I would propose a new function that starts with PyBuffer_*, maybe PyBuffer_Repr.

Then, move the implementation to some function foo.

Then, call this foo from both PyBuffer_Repr and PyBytes_Repr.