It would be useful to have a shared API for consuming bytes and bytearrays.

At present, I need to write very similar code twice. Some existing codebases only support bytes (perhaps forgetting bytearrays exist). Adding support for bytearray would be trivial if there was a shared API.

These are the functions/macros that can have "BytesOrByteArray" equivalents:
* PyBytes_Check
* PyBytes_CheckExact
* PyBytes_Size
* PyBytes_GET_SIZE
* PyBytes_AsString
* PyBytes_AS_STRING
* PyBytes_AsStringAndSize

Here are some example implementations for the macros:

#define PyBytesOrByteArray_Check(ob) (PyBytes_Check(ob) || PyByteArray_Check(ob))
#define PyBytesOrByteArray_AS_STRING(ob) (PyBytes_Check(ob) ? PyBytes_AS_STRING(ob) : PyByteArray_AS_STRING(ob))
#define PyBytesOrByteArray_GET_SIZE(ob) #define PyByteArray_GET_SIZE(self) (assert(PyBytesOrByteArray_Check(self)), Py_SIZE(self))

I remove 2.7 because this branch is in bugfix mode, no new features.

Stéphane: Please don't add me to the nosy list of bugs.

What is your use case for this? Is that something that can use the buffer API instead of these low-level APIs?

The unified C API already exists. It is called the buffer protocol.

https://docs.python.org/3/c-api/buffer.html#buffer-related-functions

My use-case is modifying existing code that supports bytes to also support bytearray.

https://github.com/mongodb/mongo-python-driver/blob/9902d239b4e557c2a657e8c8110f7751864cec95/bson/_cbsonmodule.c#L1112

The buffer protocol, which I didn't know of, feels slightly complicated for my use-case. For now I opted to adding these macros myself, only changing 3 lines.

If you need to support only bytes and bytearray, but not other bytes-like object, this is a too special case. It is easy to write your own macros or functions that wrap existing C API. Other option -- duplicate the code and replace PyBytes_ with PyByteArray_. In all cases be aware abot differences between bytes and bytearray: bytarray can change its content and size, saved values of PyByteArray_AS_STRING(ob) and PyByteArray_GET_SIZE(self) can not be used after executing arbitrary code in destructors or releasing GIT.