Double check of `PyContextVar_CheckExact` in `PyContextVar_Set`

[sobolevn]

Bug report

This code does checking for PyContextVar_CheckExact twice:

cpython/Python/context.c

Lines 340 to 350 in 1fc3039

	PyObject *
	PyContextVar_Set(PyObject *ovar, PyObject *val)
	{
	ENSURE_ContextVar(ovar, NULL)
	PyContextVar *var = (PyContextVar *)ovar;
	if (!PyContextVar_CheckExact(var)) {
	PyErr_SetString(
	PyExc_TypeError, "an instance of ContextVar was expected");
	return NULL;
	}

First in:

cpython/Python/context.c

Lines 28 to 33 in 1fc3039

	#define ENSURE_ContextVar(o, err_ret) \
	if (!PyContextVar_CheckExact(o)) { \
	PyErr_SetString(PyExc_TypeError, \
	"an instance of ContextVar was expected"); \
	return err_ret; \
	}

Then in:

cpython/Python/context.c

Lines 346 to 350 in 1fc3039

	if (!PyContextVar_CheckExact(var)) {
	PyErr_SetString(
	PyExc_TypeError, "an instance of ContextVar was expected");
	return NULL;
	}

There's no reason to do this.

Linked PRs

• gh-142873: Do not check for PyContextVar_CheckExact twice in PyContextVar_Set #142874
• [3.14] gh-142873: Do not check for PyContextVar_CheckExact twice in PyContextVar_Set (GH-142874) #142893
• [3.13] gh-142873: Do not check for PyContextVar_CheckExact twice in PyContextVar_Set (GH-142874) #142894