__text_signature__ parser doesn't handle globals in extension module

[anntzer]

BPO	37881
Nosy	@ericsnowcurrently, @anntzer

^{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 2019-08-18.13:33:56.559>
labels = ['extension-modules']
title = "__text_signature__ parser doesn't handle globals in extension module"
updated_at = <Date 2020-10-08.11:34:43.922>
user = 'https://github.com/anntzer'

bugs.python.org fields:

activity = <Date 2020-10-08.11:34:43.922>
actor = 'pitrou'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Extension Modules']
creation = <Date 2019-08-18.13:33:56.559>
creator = 'Antony.Lee'
dependencies = []
files = []
hgrepos = []
issue_num = 37881
keywords = []
message_count = 1.0
messages = ['349919']
nosy_count = 3.0
nosy_names = ['eric.snow', 'Antony.Lee', 'Eric Wieser']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue37881'
versions = []

Linked PRs

• gh-82062: correctly set module for built-in instance methods in inspect.signature() #115270

[anntzer]

Starting from the custom2 example at https://docs.python.org/3/extending/newtypes_tutorial.html#adding-data-and-methods-to-the-basic-example, change the methods table to

static PyMethodDef Custom_methods[] = {
    {"foo", (PyCFunction) Custom_foo, METH_VARARGS,
    "foo(x=ONE)\n--\n\nFoos this."
    },
    {NULL}  /* Sentinel */
};

and add a global ONE to the module dict:

    PyModule_AddObject(m, "ONE", PyLong_FromLong(1));

Building and running e.g. pydoc on this module results in

    Traceback (most recent call last):
    File ".../lib/python3.7/inspect.py", line 2003, in wrap_value
        value = eval(s, module_dict)
    File "<string>", line 1, in <module>
    NameError: name 'ONE' is not defined

    During handling of the above exception, another exception occurred:

    Traceback (most recent call last):
    File ".../lib/python3.7/inspect.py", line 2006, in wrap_value
        value = eval(s, sys_module_dict)
    File "<string>", line 1, in <module>
    NameError: name 'ONE' is not defined

    During handling of the above exception, another exception occurred:

    Traceback (most recent call last):
    File ".../lib/python3.7/runpy.py", line 193, in _run_module_as_main
        "__main__", mod_spec)
    <elided>
    File ".../lib/python3.7/inspect.py", line 2008, in wrap_value
        raise RuntimeError()
    RuntimeError

I think the fix is fairly simple; one needs to replace

    module_name = getattr(obj, '__module__', None)

in inspect.py::_signature_fromstr by

    module_name = (getattr(obj, '__module__', None)
                   or getattr(getattr(obj, '__objclass__'), '__module__', None))

(This is a less general but simpler solution than https://bugs.python.org/issue23967.)