dialog(1) like example with urwid using a single main loop.

urwid-bananas-apples-dialog.py

#!/usr/bin/env python3
import urwid
from urwid import MainLoop
import time
import sys
import os

PALETTE = [
    ('s1_titlebar', 'white,bold', 'yellow'),
    ('s2_titlebar', 'white,bold', 'light green'),
    ('fruit', 'white', 'dark blue'),
    ('filler', 'white', 'dark blue'),
    ('focus', 'white', 'dark blue'),
    ('s1_selectable', 'black', 'yellow'),
    ('s2_selectable', 'black', 'light green')
]


class Screen1Widget(urwid.WidgetWrap):
    fruit_text = """Do you like Bananas?"""

    def __init__(self, app):
        self.app = app
        self.header = urwid.AttrMap(urwid.Text('Bananas Inc.'), 's1_titlebar')
        body = urwid.AttrMap(urwid.Text(self.fruit_text), 'fruit')

        yes = urwid.Button('Yes', self.app.returncode)
        yes.rc = 0
        yes = urwid.AttrMap(yes, 'focus', 's1_selectable')

        no = urwid.Button('No', self.app.returncode)
        no.rc = 1
        no = urwid.AttrMap(no, 'focus', 's1_selectable')

        buttons = urwid.GridFlow([yes, no], 10, 3, 1, 'center')

        body = urwid.Pile([body, urwid.Divider(), buttons], focus_item=2)
        body = urwid.Filler(body, valign='top', top=1, bottom=1)
        body = urwid.AttrMap(body, 'filler')

        sfill = urwid.AttrMap(urwid.SolidFill(' '), 'filler')

        body = urwid.LineBox(body)
        body = urwid.AttrMap(body, 'filler')
        self._w = urwid.Overlay(body, sfill,
            align='center', valign='middle',
            width=('relative', 40), height=('relative', 20)
        )


class Screen2Widget(urwid.WidgetWrap):
    fruit_text = """Do you like Apples?"""

    def __init__(self, app):
        self.app = app
        self.header = urwid.AttrMap(urwid.Text('Apple Inc.'), 's2_titlebar')
        body = urwid.AttrMap(urwid.Text(self.fruit_text), 'fruit')

        yes = urwid.Button('Yes', self.app.returncode)
        yes.rc = 0
        yes = urwid.AttrMap(yes, 'focus', 's2_selectable')

        no = urwid.Button('No', self.app.returncode)
        no.rc = 1
        no = urwid.AttrMap(no, 'focus', 's2_selectable')

        buttons = urwid.GridFlow([yes, no], 10, 3, 1, 'center')

        body = urwid.Pile([body, urwid.Divider(), buttons], focus_item=2)
        body = urwid.Filler(body, valign='top', top=1, bottom=1)
        body = urwid.AttrMap(body, 'filler')

        sfill = urwid.AttrMap(urwid.SolidFill(' '), 'filler')

        body = urwid.LineBox(body)
        body = urwid.AttrMap(body, 'filler')
        self._w = urwid.Overlay(body, sfill,
            align='center', valign='middle',
            width=('relative', 40), height=('relative', 20)
        )


class App:
    def __init__(self):
        self.cur_screen_number = 0
        self.cur_screen = Screen1Widget(self)

        self.layout = urwid.Frame(
            header=self.cur_screen.header,
            body=self.cur_screen._w
        )

    def returncode(self, bt):
        if bt.rc == 0 and self.cur_screen_number == 0:
            self.cur_screen = Screen2Widget(self)
            self.layout.header = self.cur_screen.header
            self.layout.body = self.cur_screen._w
            self.cur_screen_number += 1
        elif bt.rc == 0 and self.cur_screen_number == 1:
            raise urwid.ExitMainLoop()


if __name__ == '__main__':
    app = App()
    loop = urwid.MainLoop(app.layout, PALETTE)
    loop.run()