How do I pause a loop with a button in PyGObject? - gtk

Question

I have a button that runs a loop and updates the window accordingly. I want another "pause" button that pauses this loop but it doesn't seem like I can do that while the loop is running. Perhaps threading is the solution (I tried GLib.timeout_add_seconds without success) - what is the easiest way to make this work?
I have attached my faulty code:
import sys
from time import sleep
import gi
gi.require_version("Gtk", "3.0")
from gi.repository import Gtk
class LoopButton(Gtk.Box):
def __init__(self, GUI):
Gtk.Box.__init__(self)
self.GUI = GUI
self.set_border_width(10)
self.message = "1"
button = Gtk.Button.new_with_label("Run")
button.connect("clicked", self.on_click)
self.pack_start(button, True, True, 0)
def on_click(self, widget):
msg = int(self.message)
while self.GUI.is_paused == False:
self.GUI.restart_window(str(msg))
msg += 1
while Gtk.events_pending():
Gtk.main_iteration()
sleep(1)
self.GUI.is_paused = True
class PauseButton(Gtk.Box):
def __init__(self, GUI):
Gtk.Box.__init__(self)
self.GUI = GUI
self.set_border_width(10)
button = Gtk.Button.new_with_label("Pause")
button.connect("clicked", self.on_click)
self.pack_start(button, True, True, 0)
def on_click(self, widget):
self.GUI.is_paused = True
class GUI:
def __init__(self):
self.is_paused = False
self.win = Gtk.Window()
self.window_grid = Gtk.Grid()
self.box = Gtk.Box(spacing=10)
self.label = Gtk.Label("Default label")
self.win.connect("delete-event", Gtk.main_quit)
self.start_window()
def start_window(self):
self.box.pack_start(LoopButton(self), True, True, 0)
self.box.pack_start(PauseButton(self), True, True, 0)
self.window_grid.add(self.box)
self.window_grid.add(self.label)
self.win.add(self.window_grid)
self.win.show_all()
def restart_window(self, label="Default label"):
self.window_grid.destroy()
self.window_grid = Gtk.Grid()
self.box = Gtk.Box(spacing=10)
self.label = Gtk.Label(label)
self.start_window()
def main():
app = GUI()
Gtk.main()
if __name__ == "__main__":
sys.exit(main())

Answer 1

Depending on what you really do in the loop there may be more necessary details, but below is an example of how looping is normally avoided in GLib/Gtk. The caveats of this method are: A) one iteration must be fast enough to not affect UI updates (a few milliseconds at most). B) The timing is not exact: the timeout function might not be called exactly 2 seconds after the previous call.
import gi
from gi.repository import GLib
class GUI:
def __init__(self):
# initialize the UI here...
# setup updates every two seconds
GLib.timeout_add_seconds(2, self.timeout_update)
def timeout_update(self):
# update your widgets here
print ("Updating UI now...")
# yes, we want to be called again
return True