[Python-Dev] Drop/deprecate Tkinter? (original) (raw)

Ivan Pozdeev vano at mail.mipt.ru
Thu May 3 14:24:02 EDT 2018

On 03.05.2018 20:11, Ryan Gonzalez wrote:

On May 3, 2018 11:56:24 AM MRAB <python at mrabarnett.plus.com> wrote:

On 2018-05-03 13:24, Steve Holden wrote: On Thu, May 3, 2018 at 12:12 AM, Ivan Pozdeev via Python-Dev <python-dev at python.org <mailto:python-dev at python.org>> wrote:

On 03.05.2018 1:01, Antoine Pitrou wrote: On Wed, 2 May 2018 22:54:04 +0100 Paul Moore <p.f.moore at gmail.com_ _<mailto:p.f.moore at gmail.com>> wrote: On 2 May 2018 at 22:37, Antoine Pitrou <solipsis at pitrou.net_ _<mailto:solipsis at pitrou.net>> wrote: To elaborate a bit: the OP, while angry, produced both a detailed analysis and a PR.  It's normal to be angry when an advertised feature doesn't work and it makes you lose hours of work (or, even, forces you to a wholesale redesign). Producing a detailed analysis and a PR is more than most people will ever do. His other email seems reasonable, and warrants a response, yes. But are we to take the suggestion made here (to drop tkinter) seriously, based on the fact that there's a (rare - at least it appears that the many IDLE users haven't hit it yet) race condition that causes a crash in Python 2.7? (It appears that the problem doesn't happen in the python.org <http://python.org> 3.x builds, if I understand the description of the issue). In 3.x, Tkinter+threads is broken too, albeit in a different way -- see https://bugs.python.org/issue33412 <https://bugs.python.org/issue33412> (this should've been the 2nd link in the initial message, sorry for the mix-up).

​The observation in t​hat issue that tkinter and threads should be handled in specific ways is certainly a given for old hands, who have long put the GUI code in one thread with one or more concurrent worker threads typically communicating through queues. But I haven't built anything like that recently, so I couldn't say how helpful the current documenation might be. Interacting with the GUI only in the main thread is something that I've had to do in other languages (it is/was the recommended practice), so I naturally do the same with Python and tkinter. It's also easier to reason about because you don't get elements of the GUI changing unexpectedly. To add to this, most GUI frameworks disallow modifications outside the main thread altogether. IIRC both GTK+ and Qt require this, or else it's undefined altogether. You still need some facility (coughSendMessagecough) to send update commands to the GUI (the model->view link in MVC, presenter->view in MVP). Who and how specifically carries out these commands is unimportant, an implementation detail.

Every GUI has an event/message queue exactly for that, that other threads can sent work requests into: https://doc.qt.io/qt-5.10/qcoreapplication.html#postEvent , https://developer.gnome.org/gdk3/stable/gdk3-Threads.html#gdk3-Threads.description , https://en.wikipedia.org/wiki/Event_dispatching_thread#Submitting_user_code_to_the_EDT , the aforementioned WinAPI's SendMessage() and PostMessage() just to name a few.

Tcl/Tk, being arguably the oldest usable GUI toolkit in existence, has an event queue likewise but doesn't provide a complete event loop implementation, only the building blocks for it. Tkinter fills that gap with its tk.mainloop(). It fails to provide a working means to send work into it though. Having to use a second, duplicating event queue and poll it (=busy loop) instead is an obvious crutch.

[snip]

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-- Regards, Ivan

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