[C API] Add PyBytes_Join() function

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Feature or enhancement

Python 3.13 alpha 1 removed the private _PyBytes_Join(sep, iterable) function which calls sep.join(iterable).

mypyc uses it. Since we already have PyUnicode_Join(sep, iterable), I propose to add a new PyBytes_Join() function.

In practice, it's just about renaming _PyBytes_Join() to PyBytes_Join().

Linked PRs

• gh-121646
• gh-123783

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mypyc uses it.

A code search on PyPI top 7,500 projects found 6 projects using the private _PyBytes_Join() function:

• Cython (3.0.9)
• dbnd (1.0.22.9)
• dulwich (0.21.7)
• mod_wsgi (5.0.0)
• mpi4py (3.1.5)
• mypy (1.9.0)

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mypyc uses it

Sorry, I forgot to add a reference to the mypy issue: issue gh-121489.

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Additionally, many repositories use _PyBytes_Resize as well. Perhaps that's something that should go public?

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Additionally, many repositories use _PyBytes_Resize as well. Perhaps that's something that should go public?

IMO _PyBytes_Resize() is a bad pattern, it uses a bytes object which is incomplete/inconsistent: see https://github.com/capi-workgroup/api-evolution/issues/36.

Instead, I created https://github.com/python/cpython/issues/121710: [C API] Add PyBytesWriter API.

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Implemented by the change https://github.com/python/cpython/commit/3d60dfbe1755e00ab20d0ee81281886be77ad5da.