How to duplicate blocks of widgets in kv file (

Question

I try to understand how kivy .kv files work, so I created a small application with a horizontial BoxLayout which contains three GridLayouts, as shown:

my_widget:

<my_widget@BoxLayout>:
    orientation: "horizontal"

    GridLayout:
        rows: 3
        ToggleButton:
        Image:
        Label:

    GridLayout:
        rows: 3
        ToggleButton:
        Image:
        Label:

    GridLayout:
        rows: 3
        ToggleButton:
        Image:
        Label:

No problem there, but since there are same blocks of widgets (GridLayouts) could they be duplicated? I tried something like: https://kivy.org/docs/api-kivy.lang.html

my_widget:

[my_widget2@GridLayout]:
    rows: 3
    ToggleButton:
    Image:
    Label:

<my_widget@BoxLayout>:
    orientation: "horizontal"

    my_widget2:
    my_widget2:
    my_widget2:

but didn't work. If duplicating is possible, then how can I pass information to each one widget in the block?

Answer 1

Yeah, this gets me badly everytime I encounter it e.g. copy&paste word into <> (and forget about uppercase). I still wonder if I should treat it as a bug or as a feature, because it forces user to name widgets in a correct style/case, which makes it easier for reading too.

The thing is that widgets/rules in kv language should use ThisWordStyle or something similar, but the first capital letter seems to be important. I encountered even a case when a capital letter inside the word was enough and the rest lowercase, but can't reproduce, sadly.

Words with lowercase only are mostly used as properties or variables, so maybe the my_widget was handled as a property or variable too like a global, or was completely ignored when run through the language parser.

Let's see:

1) your kv layout put into App:

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.boxlayout import BoxLayout
Builder.load_string('''
<my_widget@BoxLayout>:
    my_widget2:
    Button:
        text: 'bla'

<MyWidget>:
    my_widget:
    Button:
        text: 'bad'

<my_widget2@GridLayout>:
    rows: 3
    ToggleButton:
    Image:
    Label:

''')
class MyWidget(BoxLayout):
    pass

class Test(App):
    def build(self):
        return MyWidget()
Test().run()

The only visible thing will be a Button with 'bad' string

2) a little change in naming - my_widget -> My_widget

<My_widget@BoxLayout>:
    my_widget2:
    Button:
        text: 'bla'

<MyWidget>:
    My_widget:
    Button:
        text: 'bad'

<my_widget2@GridLayout>:
    rows: 3
    ToggleButton:
    Image:
    Label:

and there's one more visible widget!

3) a working layout with all stuff (my_widget2 -> My_widget2)

<My_widget@BoxLayout>:
    My_widget2:
    My_widget2:
    Button:
        text: 'bla'

<MyWidget>:
    My_widget:
    Button:
        text: 'bad'

<My_widget2@GridLayout>:
    rows: 3
    ToggleButton:
    Image:
    Label:

Also to answer passing arguments into such widgets (<My@Widget>), use Factory to access such widget and then it's only passing (kw)args:

#:import Factory kivy.factory.Factory
<MyWidget>:
    Button:
        on_release: root.add_widget(Factory.My_widget2(text='hi'))

<My_widget2@Label>:
    size_hint: [None, None]
    size: [200, 50]