PyObject_AsWriteBuffer is removed from CPython in 3.10

[tacaswell]

See https://github.com/python/cpython/blob/e4f1fe6edb216e04da03ae80b462ca273f00255b/Doc/whatsnew/3.10.rst#removed-1

It looks like PyObject_AsWriteBuffer is currently a wrapper around the new API (https://docs.python.org/3/c-api/objbuffer.html?highlight=pyobject_aswritebuffer#c.PyObject_AsWriteBuffer).

It looks like pycairo uses this function in one place (and wraps it to suppress the deprecation warnings)

pycairo/cairo/surface.c

Lines 823 to 825 in f0c0e5a

	PYCAIRO_BEGIN_IGNORE_DEPRECATED
	res = PyObject_AsWriteBuffer (obj, (void **)&buffer, &buffer_len);
	PYCAIRO_END_IGNORE_DEPRECATED

Unfortunately I do not have time right now to dig into this and offer a fix.

[lazka]

3.10 will become an issue once it hits beta 2021-05-03 (https://www.python.org/dev/peps/pep-0619/) so not that pressing. But thanks for bringing it up!

My first try would be to just see what PyObject_AsWriteBuffer does internally and see it it's viable to replicate that.

Here is the PR removing it from CPython: python/cpython#21117

[sarnold]

This is hitting me now in travis-ci in the Python: nightly build. Hopefully I will notice the github notifies later...

[lazka]

ok, if it affects people today we should try to look into it.

[lazka]

PyObject_AsWriteBuffer is gone in master, PyObject_AsReadBuffer still needs to be removed.