[Python-ideas] How the heck does async/await work in Python 3.5

[Terry Reedy]

On 2/27/2016 4:42 AM, Maxime S wrote:
> 2016-02-27 9:08 GMT+01:00 Terry Reedy
> <tjreedy at udel.edu
> <mailto:tjreedy at udel.edu>>:

>     It took me awhile to understand what you mean by 'tkapp'.  Instances
>     of tkinter.Tk get an undocumented .tk attribute that is an instance
>     of the undocumented and hidden _tkinter class that is called 'tkapp'
>     in printed representations.  In other words, after
>
>
> I actually meant an instance of Tk(), which also have dooneevent().
> Sorry this wasn't clear.

I was fooled because in 3.x dooneevent does not show up on the root 
completion list. 3.x Tk must have a __getattr__ that pulls attributes 
from its tk (tkapp) attribute.

# 3.5.1
 >>> import tkinter as tk
 >>> root = tk.Tk()
 >>> 'dooneevent' in tk.Tk.__dict__
False
 >>> 'dooneevent' in root.__dict__
False
 >>> root.dooneevent
<built-in method dooneevent of _tkinter.tkapp object at 0x00000210B2A64EB0>

For 2.x, dooneevent does appear as a completion, though I don't know how 
or why, as I get the same False and False as above.  (I will have to see 
if the completion code changed, or if something else changed to change 
its meaning.)

>     import tkinter as tk
>     root = tk.Tk()
>     tkapp = root.tk <http://root.tk>
>
>     tkapp has a dooneevent method.  I found the tcl doc for it at
>     https://www.tcl.tk/man/tcl/TclLib/DoOneEvent.htm
>     Does calling it with DONT_WAIT "TCL_DONT_WAIT - Do not sleep:
>     process only events that are ready at the time of the call." differ
>     from calling root.update?
>
>
> Good point. The code under update() is essentially this (plus some error
> cheking):
>
> if (nargs == 1) {
>      flags = TCL_DONT_WAIT;
> } else {
>      flags = TCL_IDLE_EVENTS;
> }
>
> while (Tcl_DoOneEvent(flags) != 0) {}

Thanks for checking this.

> So, it is probably much more efficent to call update() than to do the
> same loop in python as I did, and it avoid messing around with _tkinter
> undocumented flags.

-- 
Terry Jan Reedy