import in TYPE_CHECKING raises NameError: name 'etree' is not defined

[sector119]

Hello,

Why putting "from lxml import etree" into TYPE_CHECKING raises NameError: name 'etree' is not defined ?

from __future__ import annotations

from typing import TYPE_CHECKING

from pydantic import BaseModel

if TYPE_CHECKING:
    from lxml import etree


def mydef(value: BaseModel) -> etree._Element:
    return py2xml(value.model_dump(by_alias=True))

[abelcheung]

@sector119 Because TYPE_CHECKING would cause etree to be imported ONLY when type checker is running. You really need etree to be imported as well when running the code fragment. Remove the if TYPE_CHECKING: condition and everything should be fine.

[sector119]

But I use it only to declare return type "-> etree._Element" why shouldn't I put it in TYPE_CHECKING?
And I use "from future import annotations"

[abelcheung]

Ah, I didn't read your example code clearly. But now there are multiple possible explanations. To cause some code to do runtime check of annotation and emit NameError, pydantic might be involved. But there's pydantic and some unknown py2xml function involved, so it is impossible to pinpoint underlying problem. Do you have a minimal, self-contained working code that illustrates your problem?

[sector119]

That’s unfortunate, but it’s a bug in the Python standard library.

python/cpython#86153

Here is my traceback

Traceback (most recent call last):
File "", line 189, in _run_module_as_main
File "", line 112, in _get_module_details
File "/Users/sector119/PycharmProjects/fastapi_xmlrpc/src/fastapi_xmlrpc/init.py", line 1, in
from .applications import FastXMLRPCAPI as FastXMLRPCAPI
File "/Users/sector119/PycharmProjects/fastapi_xmlrpc/src/fastapi_xmlrpc/applications.py", line 15, in
from .lifespan import fastapi_lifespan_handler
File "/Users/sector119/PycharmProjects/fastapi_xmlrpc/src/fastapi_xmlrpc/lifespan.py", line 6, in
from fastapi_xmlrpc.routing import populate_route_examples
File "/Users/sector119/PycharmProjects/fastapi_xmlrpc/src/fastapi_xmlrpc/routing.py", line 24, in
from .examples import OpenAPIXMLRPCExample
File "/Users/sector119/PycharmProjects/fastapi_xmlrpc/src/fastapi_xmlrpc/examples.py", line 59, in
@py2xml.register
^^^^^^^^^^^^^^^
File "/Users/sector119/.local/share/uv/python/cpython-3.13.3-macos-aarch64-none/lib/python3.13/functools.py", line 905, in register
argname, cls = next(iter(get_type_hints(func).items()))
~~~~~~~~~~~~~~^^^^^^
File "/Users/sector119/.local/share/uv/python/cpython-3.13.3-macos-aarch64-none/lib/python3.13/typing.py", line 2499, in get_type_hints
hints[name] = _eval_type(value, globalns, localns, type_params)
~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/sector119/.local/share/uv/python/cpython-3.13.3-macos-aarch64-none/lib/python3.13/typing.py", line 474, in _eval_type
return t._evaluate(globalns, localns, type_params, recursive_guard=recursive_guard)
~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/sector119/.local/share/uv/python/cpython-3.13.3-macos-aarch64-none/lib/python3.13/typing.py", line 1081, in _evaluate
eval(self.forward_code, globalns, localns),
~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "", line 1, in
NameError: name 'etree' is not defined

[abelcheung]

Ah, @singledispatchmethod. So it strengthened my suspicion that runtime evaluation of annotation is involved.

The minimal example in cpython bug report contains a self-reference, thus using a string annotation is unavoidable. But in your case, I believe you can avoid exception by defining etree in runtime.

[sector119]

Yep, it works like a charm defining etree in runtime. But ruff always move that import into TYPE_CHECKING, so I should use noqa (