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Title: Argument Clinic no longer works with single optional argument
Type: behavior Stage: needs patch
Components: Argument Clinic Versions: Python 3.5
Status: closed Resolution: wont fix
Dependencies: Superseder:
Assigned To: Nosy List: larry, serhiy.storchaka
Priority: normal Keywords:

Created on 2015-04-24 13:48 by serhiy.storchaka, last changed 2022-04-11 14:58 by admin. This issue is now closed.

Messages (6)
msg241943 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2015-04-24 13:48
Argument Clinic no longer works single optional argument. For example see _tkinter.tkapp.wantobjects in the patch in issue20168.

/*[clinic input]

    value: int

[clinic start generated code]*/

It is converted to the methoddef of type METH_O.

    {"wantobjects", (PyCFunction)_tkinter_tkapp_wantobjects, METH_O, _tkinter_tkapp_wantobjects__doc__},

static PyObject *
_tkinter_tkapp_wantobjects(PyObject *self, PyObject *arg)
    PyObject *return_value = NULL;
    int group_right_1 = 0;
    int value = 0;

    if (!PyArg_Parse(arg, "i:wantobjects", &value))
        goto exit;
    return_value = _tkinter_tkapp_wantobjects_impl(self, group_right_1, value);

    return return_value;

As result wantobjects() can't be called without an argument.
msg242500 - (view) Author: Larry Hastings (larry) * (Python committer) Date: 2015-05-03 18:56
Optional groups were designed to support two specific legacy use cases:
  * functions that have groups of parameters that are 
  * functions with optional parameters to the left of required parameters

They are not intended to be used in cases like this.  I really, really wish you would stop using them except for these specific legacy cases.

Furthermore, the argument parsing for tkinter.tkapp.wantobjects has a very clear translation into Argument Clinic:

    value: int = -1

Optional groups should not be used for single-argument functions.  I have no interest in fixing this bug.
msg242501 - (view) Author: Larry Hastings (larry) * (Python committer) Date: 2015-05-03 18:59
Sorry, I forgot to finish the first bullet point.  It should have read:

  * functions that have groups of parameters that are optional only as a group (e.g. curses.window.getch)
msg242515 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2015-05-03 20:11
Then it would be better to not convert wantobjects() to Argument Clinic. Using -1 as a value for not passed argument is a hack (added in 1ab9978123be) and I don't want to propagate it to the signature.

But I afraid that there are other functions that suffer from this bug (may be in the curses module).
msg242516 - (view) Author: Larry Hastings (larry) * (Python committer) Date: 2015-05-03 20:14
If the argument currently uses a default value of -1, then I see no problem with converting it to Argument Clinic using a default value of -1.  If you claim it's a "hack" then you should discuss that with the author of 1ab9978123be.
msg242517 - (view) Author: Larry Hastings (larry) * (Python committer) Date: 2015-05-03 20:14
Closing as wontfix.  This is not a supported use of optional groups.
Date User Action Args
2022-04-11 14:58:16adminsetgithub: 68239
2015-05-03 20:14:52larrysetstatus: languishing -> closed
resolution: wont fix
messages: + msg242517
2015-05-03 20:14:20larrysetmessages: + msg242516
2015-05-03 20:11:23serhiy.storchakasetstatus: open -> languishing

messages: + msg242515
2015-05-03 18:59:29larrysetmessages: + msg242501
2015-05-03 18:56:08larrysetmessages: + msg242500
2015-05-03 14:31:49serhiy.storchakaunlinkissue20168 dependencies
2015-04-24 13:49:13serhiy.storchakalinkissue20168 dependencies
2015-04-24 13:48:50serhiy.storchakacreate