`inspect.getfullargspec` isn't ready for deferred evaluation of annotations

[jacobtylerwalls]

Bug report

Bug description:

inspect.getfullargspec isn't compatible with 3.14 signatures that depend on deferred evaluation of annotations, and doesn't expose an argument to pass through annotationlib.Format.FORWARDREF to prevent the failure.

import inspect
from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from collections.abc import Iterable

def func(a: Iterable):
    return

inspect.getfullargspec(func)

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.14/lib/python3.14/inspect.py", line 1261, in getfullargspec
    sig = _signature_from_callable(func,
                                   follow_wrapper_chains=False,
                                   skip_bound_arg=False,
                                   sigcls=Signature,
                                   eval_str=False)
  File "/Library/Frameworks/Python.framework/Versions/3.14/lib/python3.14/inspect.py", line 2502, in _signature_from_callable
    return _signature_from_function(sigcls, obj,
                                    skip_bound_arg=skip_bound_arg,
                                    globals=globals, locals=locals, eval_str=eval_str,
                                    annotation_format=annotation_format)
  File "/Library/Frameworks/Python.framework/Versions/3.14/lib/python3.14/inspect.py", line 2325, in _signature_from_function
    annotations = get_annotations(func, globals=globals, locals=locals, eval_str=eval_str,
                                  format=annotation_format)
  File "/Library/Frameworks/Python.framework/Versions/3.14/lib/python3.14/annotationlib.py", line 890, in get_annotations
    ann = _get_dunder_annotations(obj)
  File "/Library/Frameworks/Python.framework/Versions/3.14/lib/python3.14/annotationlib.py", line 1059, in _get_dunder_annotations
    ann = getattr(obj, "__annotations__", None)
  File "<stdin>", line 1, in __annotate__
    def func(a: Iterable):
                ^^^^^^^^
NameError: name 'Iterable' is not defined

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    inspect.getfullargspec(func)
    ~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.14/lib/python3.14/inspect.py", line 1271, in getfullargspec
    raise TypeError('unsupported callable') from ex
TypeError: unsupported callable

---

I know getfullargspec() is threatened with deprecation (#108901, #76371), but over at Django we're going to need to build a "safe" version of this function (or migrate away from it entirely) unless an upstream patch makes more sense.

I presume that's either:

• always passing through annotationlib.Format.FORWARDREF to inspect.Signature
• exposing an argument

Defensively always using FORWARDREF or similar seems simplest. Happy to provide a PR.

CPython versions tested on:

3.14

Operating systems tested on:

macOS

Linked PRs

• gh-141560: Add annotation_format parameter to getfullargspec #149457

[anaghaaaaa9]

Hey i would like to start working on this, can I take up this issue and start working ?

[picnixz]

We first need to assess whether this is an issue or not and how to address it. cc @JelleZijlstra

[anaghaaaaa9]

sure , i will review the codebase and keep an eye on the issue. If it requires a fix i will be ready to contribute

[picnixz]

I do not think it is necessary to review the codebase. I prefer first hearing from Jelle as he is the one who implemented deferred annotations. If you want an easy issue to contribute to, I suggest looking at the issues with the easy label.

[JelleZijlstra]

We do need to change something here. Perhaps the most consistent way to do it would have been to make inspect.Parameter.annotation and inspect.FullArgSpec.annotation also lazily evaluated, but I didn't think of that for 3.14.

Other options include adding an annotation_format parameter to fullargspec, and making it just eat the exception if the annotations can't be evaluated.

What I like about the first suggestion is that likely many users of getfullargspec (or inspect.signature) don't care about the annotations, so if we make them lazily evaluated, they won't have to worry about the problem at all.