Inconsistent TypeError messages with callables

[Tapeline]

Bug report

Bug description:

Consider this example:

>>> class A:
...     def __str__(self): return "some random text"
...     def __call__(self, a): ...

>>> A()()
Traceback (most recent call last):
  File "<python-input-16>", line 1, in <module>
    A()()
    ~~~^^
TypeError: A.__call__() missing 1 required positional argument: 'a'

>>> A()(*None)
Traceback (most recent call last):
  File "<python-input-17>", line 1, in <module>
    A()(*None)
    ~~~^^^^^^^
TypeError: some random text argument after * must be an iterable, not NoneType

The first one gets the callable's __qualname__. The second, on the other hand, does not, but should do so.

Another example, mentioned in #135975 (issuecomment link):

>>> exit(*None)
Traceback (most recent call last):
  File "<python-input-0>", line 1, in <module>
    exit(*None)
    ~~~~^^^^^^^
TypeError: Use exit() or Ctrl-Z plus Return to exit argument after * must be an iterable, not NoneType

Which just gets the exit's __repr__.

If this is recognized as unwanted behaviour, I'm ready to make a PR.

CPython versions tested on:

3.13

Operating systems tested on:

Windows

Edit: ** also does not work properly:

# the code from the first example
>>> A()(**1)
Traceback (most recent call last):
  File "<python-input-26>", line 1, in <module>
    A()(**1)
    ~~~^^^^^
TypeError: some random text argument after ** must be a mapping, not int

Linked PRs

• gh-136327: Fix inconsistent TypeError messages regarding invalid values after * and ** #136395

[sobolevn]

If this is recognized as unwanted behaviour, I'm ready to make a PR.

Please, go ahead :)
I would love to review it!

[Tapeline]

I've done some investigation on this bug. Seems that it's harder, than I initially thought.

The function's name is received via _PyObject_FunctionStr, which indeed gets the function's qualname. If the qualname isn't present, it just gets whatever is in __str__/__repr__ of the function.

Regarding the examples I've shown earlier:

1. Example with exit is behaving this way, because some objects in __builtins__ for some reason do not have the __qualname__ attribute. Here's the full list:

Ellipsis
False
None
NotImplemented
True
_
__debug__
__doc__
__name__
__package__
__spec__
copyright
credits
exit
help
license
quit

I'm not quite sure about the dunder ones, but all others definetly should have a qualname.

2. The example with the class, on the other hand works that way, because the constructed object is passed as a function into _PyObject_FunctionStr. Since it does not have a __qualname__, it defaults to whatever is in __str__/__repr__ of that object. Possible solution would be to just add an edge-case handler to _PyObject_FunctionStr: if an object is not an instance of function or builtin_function_or_method, then we try searching in object.__call__.