Tkinter messagebox and using datetime/timedelta

[Yoriz]

Example of using the after method to do something after every second without blocking the GUI event loop.

import tkinter as tk
from tkinter import messagebox
import datetime as dt


class MainFrame(tk.Frame):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        theLabel = tk.Label(self, text="Enter time below in minutes (e.g 30)")
        theLabel.pack()
        self.entry_1 = tk.Entry(self)
        self.entry_1.pack()
        button_1 = tk.Button(self, text="Set interval",
                             command=self.set_alarm_time)
        button_1.pack()
        self.timenow_label = tk.Label(self)
        self.timenow_label.pack()
        self.alarm_time_label = tk.Label(self, text='Alarm time:')
        self.alarm_time_label.pack()
        self.pack()
        self.alarm_time = None
        self.timer()

    def set_alarm_time(self):
        try:
            interval = dt.timedelta(minutes=int(self.entry_1.get()))
        except ValueError:
            self.entry_1.delete(0, tk.END)
            messagebox.showinfo(
                'Entry error', message="Please enter an integer")
            return

        self.alarm_time = dt.datetime.now() + interval
        self.alarm_time_label['text'] = self.alarm_time.strftime(
            'Alarm time: %H:%M:%S')

    def timer(self):
        timenow = dt.datetime.now()
        self.timenow_label['text'] = timenow.strftime('Time now: %H:%M:%S')
        if self.alarm_time and timenow >= self.alarm_time:
            self.alarm_time = None
            self.alarm_time_label['text'] = 'Alarm time:'
            self.entry_1.delete(0, tk.END)
            messagebox.showinfo(
                'STRETCH TIME', message="Please take a stretch break!")

        self.after(1000, self.timer)


if __name__ == "__main__":
    app = tk.Tk()
    main_frame = MainFrame()
    app.mainloop()