[PyQt] Bug (and fix!): laggy interactive input on Windows

[Phil Thompson]

On 22/10/2014 6:51 pm, Chris Billington wrote:
> To whom it may concern,
> 
> The input hook function qtcore_input_hook() in
> sip/QtCore/qcoreapplication.sip appears to be the cause of laggy
> interactive input on Windows my colleagues and I been seeing. This 
> mostly
> comes up when using matplotlib interactively with the PyQt backend 
> (default
> in popular Windows Python distributions) - input keystrokes lag behind 
> by
> some significant fraction of a second, making things pretty unusable.
> 
> If one reduces the timeout in qtcore_input_hook()from 100ms to 10ms, 
> the
> lag becomes completely unnoticeable and input is responsive once more. 
> This
> increases Python's idle CPU usage from 0.03% to 0.3% on my machine.
> 
> Attached is a script that demonstrates this in Python, and patches for
> sip/QtCore/qcoreapplication.sip to reduce the timeout (If I have given
> these patches in the wrong format I apologize - it is a single 
> character
> deletion so maybe providing patches is silly anyway).
> 
> This applies to both PyQt4 and PyQt5.

Did you experiment to find 10 as the best, or did you pick it at random 
and it happened to work?

I just don't want to reduce it any more than necessary.

Thanks,
Phil