Python/Kivy : How to put dynamic label widget and value

Question

I have two file test.py and test.kv .
i run test.py then shows show button.
When i click on show button then def abc call.Can someone tell me how to show array in dynamic label and value(Item1=5000.Item2=1000).
Item1 5000
Item2 1000

I am using array
arr = ({'Item1': 5000},{'Item2': 1000})

test.py

from kivy.uix.screenmanager import Screen
from kivy.app import App
from kivy.lang import Builder
from kivy.core.window import Window
from kivy.properties import BooleanProperty, ListProperty, StringProperty, ObjectProperty, NumericProperty

Window.clearcolor = (0.5, 0.5, 0.5, 1)
Window.size = (600, 600)

class Invoice(Screen):
    def __init__(self, **kwargs):
        super(Invoice, self).__init__(**kwargs)

    def abc(self):
        #fetching from database
        arr = ({'Item1': 5000},{'Item2': 1000})
        print(arr)

class Test(App):

    def build(self):
        self.root = Builder.load_file('test.kv')
        return self.root


if __name__ == '__main__':
    Test().run()

test.kv

<Button@Button>:
    font_size: 15
    font_name: 'Verdana'
    size_hint_y:None
    height: 30

<Label@Label>:
    font_size: 15
    font_name: 'Verdana'
    size_hint_y:None
    height: 30

Invoice:
    BoxLayout:
        orientation: "vertical"
        padding : 15, 15

        BoxLayout:
            orientation: "vertical"
            padding : 5, 5
            size_hint: .6, None
            pos_hint: {'x': .18,}


            BoxLayout:
                orientation: "horizontal"
                padding : 5, 5
                spacing: 10, 10
                size: 800, 40
                size_hint: 1, None

                Button:
                    text: "Show"
                    size_hint_x: .05
                    spacing_x: 30
                    on_press:root.abc()

        BoxLayout:
            orientation: "horizontal"
            size_hint: 1, 1

            BoxLayout:
                orientation: "vertical"
                size_hint: .5, 1
                padding : 0, 15
                spacing: 10, 10
                size: 500, 30

                Button:
                    text: "Invoice"
                    text_size: self.size
                    halign: 'center'
                    valign: 'middle'

                GridLayout:
                    cols: 2
                    #orientation: "horizontal"
                    padding : 5, 0
                    spacing: 10, 0
                    #size: 500, 30
                    size_hint: 1, 1
                    pos: self.pos
                    size: self.size

                    Label:
                        size_hint_x: .35
                        text: "Item1"
                        text_size: self.size
                        halign: 'left'
                        valign: 'middle'
                        canvas.before:
                            Color:
                                rgb: .6, .6, .6
                            Rectangle:
                                pos: self.pos
                                size: self.size

                    Label:
                        size_hint_x: .15
                        text: "5000"
                        text_size: self.size
                        halign: 'right'
                        valign: 'middle'
                        canvas.before:
                            Color:
                                rgb: .6, .6, .6
                            Rectangle:
                                pos: self.pos
                                size: self.size

Answer 1

In your abc() method you can create labels and add them to your layout. In order to do that, I made a few change to your code. I added an id to your GridLayout and changed your custom label class to MyLabel and added it to the py file, so that I could create them in Python. Here is the modified Python file:

from kivy.uix.label import Label
from kivy.uix.screenmanager import Screen
from kivy.app import App
from kivy.lang import Builder
from kivy.core.window import Window

Window.clearcolor = (0.5, 0.5, 0.5, 1)
Window.size = (600, 600)

class MyLabel(Label):
    pass

class Invoice(Screen):
    def __init__(self, **kwargs):
        super(Invoice, self).__init__(**kwargs)

    def abc(self):
        #fetching from database
        arr = ({'Item1': 5000},{'Item2': 1000})
        layout = self.ids['invoices']
        for invoice in arr:
            for key,val in invoice.items():
                lab1 = MyLabel(text=str(key),size_hint_x=.35, halign='left' )
                lab2 = MyLabel(text=str(val),size_hint_x=.15, halign='right' )
                layout.add_widget(lab1)
                layout.add_widget(lab2)

class Test(App):

    def build(self):
        self.root = Builder.load_file('test.kv')
        return self.root

And changes to the kv file included changing Label to MyLabel, moving as much as possible to the MyLabel class, and removing your example labels:

<Button@Button>:
    font_size: 15
    font_name: 'Verdana'
    size_hint_y:None
    height: 30

<MyLabel>:
    font_size: 15
    font_name: 'Verdana'
    size_hint_y:None
    height: 30
    text_size: self.size
    valign: 'middle'
    canvas.before:
        Color:
            rgb: .6, .6, .6
        Rectangle:
            pos: self.pos
            size: self.size

Invoice:
    BoxLayout:
        orientation: "vertical"
        padding : 15, 15

        BoxLayout:
            orientation: "vertical"
            padding : 5, 5
            size_hint: .6, None
            pos_hint: {'x': .18,}


            BoxLayout:
                orientation: "horizontal"
                padding : 5, 5
                spacing: 10, 10
                size: 800, 40
                size_hint: 1, None

                Button:
                    text: "Show"
                    size_hint_x: .05
                    spacing_x: 30
                    on_press:root.abc()

        BoxLayout:
            orientation: "horizontal"
            size_hint: 1, 1

            BoxLayout:
                orientation: "vertical"
                size_hint: .5, 1
                padding : 0, 15
                spacing: 10, 10
                size: 500, 30

                Button:
                    text: "Invoice"
                    text_size: self.size
                    halign: 'center'
                    valign: 'middle'

                GridLayout:
                    id: invoices
                    cols: 2
                    #orientation: "horizontal"
                    padding : 5, 0
                    spacing: 10, 0
                    #size: 500, 30
                    size_hint: 1, 1
                    pos: self.pos
                    size: self.size