Kivy: how to define which Tab is to be active on opening a TabbedPanel

Question

how do I define which tab is active when opening a TabbedPanel?

Here I'm using tabs along the left side, and so want tab #3 to be active at the start, not tab #1.

import kivy, os
from  kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import Screen
from kivy.base import runTouchApp


Builder.load_string("""

<TabbedTestScreen>:

    TabbedPanel:
        do_default_tab: False
        tab_pos: 'left_top'
        tab_height: 90
        tab_width: 90

        TabbedPanelItem:
            text: '1'
            Label:
                text: '1'
        TabbedPanelItem:
            text: '2'
            Label:
                text: '2'
        TabbedPanelItem:
            text: '3' 
            id: home_tab
            Label:
                text: '3'                    

""")

class TabbedTestScreen(Screen):
    pass

runTouchApp(TabbedTestScreen())

Answer 1

You can use switch_to to do this at the initialization of your class:

from  kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import Screen
from kivy.base import runTouchApp
from kivy.properties import ObjectProperty
from kivy.clock import Clock



Builder.load_string("""

<TabbedTestScreen>:
    tab_panel: tab_panel
    home_tab: home_tab
    TabbedPanel:
        id: tab_panel
        do_default_tab: False
        tab_pos: 'left_top'
        tab_height: 90
        tab_width: 90

        TabbedPanelItem:
            text: '1'
            Label:
                text: '1'
        TabbedPanelItem:
            text: '2'
            Label:
                text: '2'
        TabbedPanelItem:
            text: '3' 
            id: home_tab
            Label:
                text: '3'                    
""")

class TabbedTestScreen(Screen):
    tab_panel = ObjectProperty(None)
    home_tab = ObjectProperty(None)

    def __init__(self, **kwargs):
        super(TabbedTestScreen, self).__init__(**kwargs)
        Clock.schedule_once(lambda *args: self.tab_panel.switch_to(self.home_tab))



runTouchApp(TabbedTestScreen())