termios.tpsetattr does rewrite errors

[sobolevn]

Bug report

This code is problematic:

cpython/Modules/termios.c

Lines 215 to 224 in bf4bc36

	mode.c_iflag = (tcflag_t) PyLong_AsLong(PyList_GetItem(term, 0));
	mode.c_oflag = (tcflag_t) PyLong_AsLong(PyList_GetItem(term, 1));
	mode.c_cflag = (tcflag_t) PyLong_AsLong(PyList_GetItem(term, 2));
	mode.c_lflag = (tcflag_t) PyLong_AsLong(PyList_GetItem(term, 3));
	speed_t ispeed = (speed_t) PyLong_AsLong(PyList_GetItem(term, 4));
	speed_t ospeed = (speed_t) PyLong_AsLong(PyList_GetItem(term, 5));
	PyObject *cc = PyList_GetItem(term, 6);
	if (PyErr_Occurred()) {
	return NULL;
	}

It does rewrite errors that happened before. Showing the last error, not the first one.
This goes against Python's semantics.

Here's the reproducer:

>>> import termios

>>> termios.tcsetattr(0, 0, [0, 1, 2, '3', 4, 5, 6])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'str' object cannot be interpreted as an integer

>>> termios.tcsetattr(0, 0, [object(), 1, 2, '3', 4, 5, 6])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'str' object cannot be interpreted as an integer

The second error should say:

>>> termios.tcsetattr(0, 0, [object(), 1, 2, '3', 4, 5, 6])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'object' object cannot be interpreted as an integer

And while we are there we can also change PyList_GetItem to PyList_GET_ITEM, because:

• term is known to be a list
• the size of term is known to be 7
  See check

  cpython/Modules/termios.c

  Lines 197 to 201 in bf4bc36

  	if (!PyList_Check(term) || PyList_Size(term) != 7) {
  	PyErr_SetString(PyExc_TypeError,
  	"tcsetattr, arg 3: must be 7 element list");
  	return NULL;
  	}

  before these lines.

The only problem is tests. I think that termios is not tested that much in our suite. We don't even have test_termios.py file. Should I add one?

Refs #110260

Linked PRs

• gh-110365: Fix error overwrite in termios.tcsetattr #110366
• [3.12] gh-110365: Fix error overwrite in termios.tcsetattr (GH-110366) #110389
• [3.11] gh-110365: Fix error overwrite in termios.tcsetattr (GH-110366) #110390