ElementTree.Element.extend: bad error message when error occurs in generator

[goodmami]

BPO	45686
Nosy	@goodmami

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-11-02.00:50:51.579>
labels = ['expert-XML', 'type-bug', '3.9', '3.10', '3.11']
title = 'ElementTree.Element.extend: bad error message when error occurs in generator'
updated_at = <Date 2022-01-15.16:31:14.321>
user = 'https://github.com/goodmami'

bugs.python.org fields:

activity = <Date 2022-01-15.16:31:14.321>
actor = 'iritkatriel'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['XML']
creation = <Date 2021-11-02.00:50:51.579>
creator = 'goodmami'
dependencies = []
files = []
hgrepos = []
issue_num = 45686
keywords = []
message_count = 1.0
messages = ['405476']
nosy_count = 1.0
nosy_names = ['goodmami']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue45686'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

[goodmami]

Both the Python and C versions of xml.etree.ElementTree allow Element.extend() to accept a sequence or an iterable, such as a generator expression (although the docs only mention "sequence"; that's a separate problem):

>> from xml.etree import ElementTree as ET
>> elem = ET.Element('root')
>> elem.extend(ET.Element('child') for _ in range(3))
>> pyelem = ET._Element_Py('root')
>> pyelem.extend(ET._Element_Py('child') for _ in range(3))

If the generator expression raises an Exception (for instance, by omitting the tag name as below), then the Python implementation passes up the error:

>>> pyelem.extend(ET._Element_Py() for _ in range(3))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.9/xml/etree/ElementTree.py", line 253, in extend
    for element in elements:
  File "<stdin>", line 1, in <genexpr>
TypeError: __init__() missing 1 required positional argument: 'tag'

But the C implementation hides it with a misleading exception of its own:

>>> elem.extend(ET.Element() for _ in range(3))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: expected sequence, not "generator"

Is it possible to pass up the original exception, as in the Python implementation? In the C code, the exception is raised when PySequence_Fast returns something false:

    seq = PySequence_Fast(elements, "");
    if (!seq) {
        PyErr_Format(
            PyExc_TypeError,
            "expected sequence, not \"%.200s\"", Py_TYPE(elements)->tp_name
            );
        return NULL;
    }

Otherwise, while it would be good if the error message didn't incorrectly state that Element.extend() requires a sequence and not a generator, it currently leads the programmer to the actual error. That is, when the programmer tries to make the argument a sequence by creating a list, the error will be propagated before Element.extend() is called:

>>> elem.extend([ET.Element() for _ in range(3)])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 1, in <listcomp>
TypeError: Element() takes at least 1 argument (0 given)