tkinter's after() AttributeError with functools.partial (no attribute __name__)

[philtgd]

BPO	44404
Nosy	@terryjreedy, @serhiy-storchaka, @miss-islington, @E-Paine
PRs	bpo-44404: tkinter after support callable classes #26812 [3.10] bpo-44404: tkinter after support callable classes (GH-26812) #26921

^{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 = <Date 2021-06-27.08:05:21.961>
created_at = <Date 2021-06-12.20:53:12.881>
labels = ['type-feature', 'expert-tkinter', '3.10', '3.11']
title = "tkinter's after() AttributeError with functools.partial (no attribute __name__)"
updated_at = <Date 2021-06-27.09:34:21.582>
user = 'https://bugs.python.org/philtgd'

bugs.python.org fields:

activity = <Date 2021-06-27.09:34:21.582>
actor = 'epaine'
assignee = 'none'
closed = True
closed_date = <Date 2021-06-27.08:05:21.961>
closer = 'serhiy.storchaka'
components = ['Tkinter']
creation = <Date 2021-06-12.20:53:12.881>
creator = 'phil.tgd'
dependencies = []
files = []
hgrepos = []
issue_num = 44404
keywords = ['patch']
message_count = 11.0
messages = ['395712', '395735', '396095', '396407', '396408', '396434', '396556', '396560', '396564', '396565', '396570']
nosy_count = 5.0
nosy_names = ['terry.reedy', 'serhiy.storchaka', 'miss-islington', 'epaine', 'phil.tgd']
pr_nums = ['26812', '26921']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue44404'
versions = ['Python 3.10', 'Python 3.11']

[philtgd]

>>> import tkinter
>>> from functools import partial
>>> r=tkinter.Tk()
>>> r.after(500, partial(print, "lol"))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.7/tkinter/__init__.py", line 755, in after
    callit.__name__ = func.__name__
AttributeError: 'functools.partial' object has no attribute '__name__'

[E-Paine]

Reproducible in Python 3.9. The issue occurs because functools.partial is a class, not function. I believe the fix is simply something like:

try:
callit.__name__ = func.__name__
except AttributeError:
callit.__name__ = type(func).__name__

This will use the name 'partial'. The lack of '__name__' is noted in the functools docs so I agree with Philip that this is an issue with tkinter. Philip, do you want to open a pull request for this?

It should be noted that functools.partial is not required in this situation as 'after' takes arguments for the function call:
r.after(500, print, "lol")

[terryjreedy]

The docstring for .after says the 2nd argument must be a 'function'. Whether this issue is a bugfix or enhancement request depends whether one interprets 'function' as 'callable' or something narrower that only includes objects that necessarily have __name__ attributes. The latter would exclude partials and instances of user classes with __call__ methods.

While a one-time-use partial as in the example is superfluous, I think other uses and parameterized callback classes should be supported. So I agree with changing the tkinter code rather than qualifying 'function' with 'has a .__name__ attribute'. I think 'type(func).__name__' should be safe.

[serhiy-storchaka]

New changeset e9c8f78 by E-Paine in branch 'main':
bpo-44404: tkinter after support callable classes (GH-26812)
e9c8f78

[serhiy-storchaka]

It is on borderline between new feature and bugfix (depends on your interpretation of the documentation), so I decided to backport it to not yet released 3.10, but not to 3.9 which has been already used for a year.

[terryjreedy]

I was thinking the same.

[E-Paine]

Can this issue be closed?

[terryjreedy]

When the backport is done or Serhiy changes his mind.

Can you change labels on your own PRs?

[miss-islington]

New changeset e1f3bd2 by Miss Islington (bot) in branch '3.10':
bpo-44404: tkinter after support callable classes (GH-26812)
e1f3bd2

[serhiy-storchaka]

There were some issues with the backporting bot. Seems they were temporary.

Thank you for your contribution E. Paine. For this issue and others.

[E-Paine]

Can you change labels on your own PRs?

Sadly not (hence why I need to ask for e.g. skip news)