Demo showing how to generate a popup from a thread

DemoPrograms/Demo_Multithreaded_Calling_Popup.py

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+import threading
+import time
+import PySimpleGUI as sg
+
+"""
+    Threaded Demo - Uses Window.write_event_value to communicate from thread to GUI
+    
+    A demo specifically to show how to use write_event_value to
+        "show a popup from a thread"
+        
+    You cannot make any direct calls into PySimpleGUI from a thread
+    except for Window.write_event_value()
+    Cuation - This method still has a risk of tkinter crashing
+    
+    Copyright 2021 PySimpleGUI
+"""
+
+
+def the_thread(window:sg.Window, seconds):
+    """
+    The thread that communicates with the application through the window's events.
+
+    Wakes every X seconds that are provided by user in the main GUI:
+        Sends an event to the main thread
+        Goes back to sleep
+    """
+    i = 0
+    while True:
+        time.sleep(seconds)
+        # send a message to the main GUI. It will be read using window.read()
+        # the "Value" send is a tuple that contains all the things to show in the popup
+        window.write_event_value('-POPUP-',
+                                 ('Hello this is the thread...',
+                                  f'My counter is {i}',
+                                  f'Will send another message in {seconds} seconds'))
+        i += 1
+
+
+def main():
+    """
+    Every time "Start A Thread" is clicked a new thread is started
+    When the event is received from the thread, a popup is shown in its behalf
+    """
+
+    layout = [  [sg.Output(size=(60,10))],
+                [sg.T('How often a thread will show a popup in seconds'),
+                 sg.Spin((2, 5, 10, 20), initial_value=5, k='-SPIN-')],
+                [sg.B('Start A Thread'), sg.B('Dummy'), sg.Button('Exit')]  ]
+
+    window = sg.Window('Window Title', layout, finalize=True, font='_ 15')
+
+
+    while True:             # Event Loop
+        event, values = window.read()
+        print(event, values)
+        if event == sg.WIN_CLOSED or event == 'Exit':
+            break
+        if event == '-POPUP-':
+            sg.popup_non_blocking('This is a popup that the thread wants to show',
+                     *values['-POPUP-'])
+        elif event == 'Start A Thread':
+            print(f'Starting thread.  You will see a new popup every {values["-SPIN-"]} seconds')
+            threading.Thread(target=the_thread, args=(window, values['-SPIN-']), daemon=True).start()
+
+    window.close()
+
+
+if __name__ == '__main__':
+    main()