QName doesn't work with iterators

[Xavier (Open ERP)]

The documentation of QName (https://lxml.de/api/lxml.etree.QName-class.html) states:

> You can pass QName objects wherever a tag name is expected.

The signature of `_Element.iter` is defined as:

> iter(self, tag=None, *tags)

from this one would expect to pass a QName directly to iter would work and filter on that qname, however

    t = etree.fromstring("<root/>")
    for node in t.iter(QName('http://example.org/ns', 'a')):
        ...

instead of doing nothing raises "TypeError: 'lxml.etree.QName' object is not iterable".

Workaround: str(QName(...)) but that's not great, and the documentation is still not correct.

Environment:

Python : sys.version_info(major=3, minor=6, micro=9, releaselevel='final', serial=0)
lxml.etree : (4, 5, 0, 0)
libxml used : (2, 9, 10)
libxml compiled : (2, 9, 10)
libxslt used : (1, 1, 34)
libxslt compiled : (1, 1, 34)

[scoder (scoder)]

Ah, yes, thanks for the report. The MultiTagMatcher needs to unpack QNames here:

https://github.com/lxml/lxml/blob/41cc5f378e2454ff1cabe5d227242cce211a3a2b/src/lxml/etree.pyx#L2720

I would just let it create the string and recurse. This is not performance critical at all.
PR welcome, including tests, which should go near the".iter()" tests in "test_etree.py".

[Xavier (Open ERP) (xmo-deactivatedaccount)]

Looking at the qname definition it looks like all that'd be necessary would be an

    elif tag is QName:
        if tag.text in seen:
            return
        seen.add(tag.text)
        self._py_tags.append((tag.namespace or '', tag.localname))

does that seem right?

[scoder (scoder)]

I would literally go for

    elif isinstance(tag, QName):
        self._storeTags(self, tag.text, seen)

[Xavier (Open ERP) (xmo-deactivatedaccount)]

Created https://github.com/lxml/lxml/pull/298