TypeError: descriptor '__subclasses__' of 'type' object needs an argument

[zallek]

Hi,

I have a TypeError when I try to upgrade the xsdata from 20.10 to 20.11.
We use python 3.7.9

With the 20.11, the lib is falling to get the subclasses of the following class
https://github.com/pallets/flask-sqlalchemy/blob/9876d6c0ec3ac3390f739bb3eb3ea5ab4c0905b7/src/flask_sqlalchemy/model.py#L121

The trackback

Error
Traceback (most recent call last):
  File "/Users/nicolasfortin/.pyenv/versions/3.7.9/lib/python3.7/unittest/case.py", line 59, in testPartExecutor
    yield
  File "/Users/nicolasfortin/.pyenv/versions/3.7.9/lib/python3.7/unittest/case.py", line 628, in run
    testMethod()
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/components/be_core/claim_management/services/assur_card/tests/test_assur_card_parser.py", line 45, in test_parse_assur_pharma_file_invoice
    invoice = AssurCardParser.parse_assur_pharma_file_invoice(f.read())
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/components/be_core/claim_management/services/assur_card/assur_card_parser.py", line 63, in parse_assur_pharma_file_invoice
    return parser.from_string(invoice, SingleMessage)
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/bindings.py", line 24, in from_string
    return self.from_bytes(source.encode(), clazz)
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/bindings.py", line 28, in from_bytes
    return self.parse(io.BytesIO(source), clazz)
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/dataclass/parsers/nodes.py", line 464, in parse
    result = handler.parse(source)
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/dataclass/parsers/handlers/lxml.py", line 37, in parse
    return self.process_context(ctx)
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/dataclass/parsers/handlers/lxml.py", line 50, in process_context
    element.nsmap,
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/dataclass/parsers/xml.py", line 46, in start
    super().start(clazz, queue, objects, qname, attrs, ns_map)
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/dataclass/parsers/nodes.py", line 483, in start
    child = item.child(qname, attrs, ns_map, len(objects))
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/dataclass/parsers/nodes.py", line 114, in child
    node = self.build_node(var, attrs, ns_map, position)
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/dataclass/parsers/nodes.py", line 136, in build_node
    var.clazz, attrs, ns_map, position, var.derived
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/dataclass/parsers/nodes.py", line 191, in build_element_node
    meta = self.context.fetch(clazz, self.meta.namespace, xsi_type)
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/dataclass/context.py", line 67, in fetch
    subclass = self.find_subclass(clazz, xsi_type)
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/dataclass/context.py", line 111, in find_subclass
    types = self.find_types(qname)
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/dataclass/context.py", line 95, in find_types
    self.build_xsi_cache()
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/dataclass/context.py", line 75, in build_xsi_cache
    for clazz in self.get_subclasses(object):
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/dataclass/context.py", line 360, in get_subclasses
    yield subclass
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/dataclass/context.py", line 360, in get_subclasses
    yield subclass
  File "/Users/nicolasfortin/Workspaces/Alan/alan-backend/.venv/lib/python3.7/site-packages/xsdata/formats/dataclass/context.py", line 359, in get_subclasses
    yield from cls.get_subclasses(subclass)
TypeError: descriptor '__subclasses__' of 'type' object needs an argument

[tefra]

Hi @zallek thanks for reporting, I just released a fix to catch all type errors when its building the xsi cache.

Unfortunately I failed to reproduced it correctly, can you share more info like your other project dependencies and os.

I created a venv with python 3.7.9, installed the flask-sqlalchemy and imported the module you mentioned in one of the tests that's triggering the xsi cache rebuild but I didn't get the exception, the previous check in that method actually worked as it was supposed to.

[zallek]

Your fix works for us. Thank you.