Will check with another linux distribution.
It's just the grab_focus that seems not working. Because i made a test with a 'entry.set_text('TEST')' and it's correctly displaying value on the first entry field. But i have to click on this entry to have focus...
I have tested with GTK 3.24.3 and gnome/mutter on Manjaro and I have the same behavior.
The focus is not set on the entry field.
But I have tested with GTK Client 5.0.5 on Windows 10 PRO. It's working even without patch.
There seems to be something wrong with your window manager. The code ask to put the focus and cursor on the window and the WM does not do it. I do not see what we can do more.
I have installed a Ubuntu 18.04 LTS.
I only install tryton GTK Client with pip3 install tryton (5.0.5)
I connect to demo5.0.tryton.org and I have the same behaviour.
The focus is not on the first text entry.
Well I think the Ubuntu WM is not the best choice. It is known to break behavior (like with the top menu bar).
I'm pretty sure it is because it force the focus to stay under the cursor.
Fedora with KDE - Kwin : Ok the behavior is good
Fedora with MATE - Metacity : Ok the behavior is good
Fedora with GNOME - Gnome-shell : NOK the focus is not set on the first entry
Manjaro with XFCE - Xfwm4 : NOK the focus is not set on the first entry
it's a behavior problem with the window manager but not only gnome-shell.
I think the solution is to use a Popover [1]. This widget did not exist in GTK+2 and what we tried to do with the filter window is indeed what Popover solved.