#-----------main.py


from kivy.garden.matplotlib.backend_kivyagg import FigureCanvasKivyAgg
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
import matplotlib.pyplot as plt
import numpy as np

from kivy_garden.graph import Graph, MeshLinePlot
from kivy.uix.tabbedpanel import TabbedPanel
from kivy.lang import Builder
from kivy.uix.relativelayout import RelativeLayout
from kivy.uix.floatlayout import FloatLayout
from kivy.properties import ObjectProperty



Builder.load_file('tab.kv')


class Plot(TabbedPanel):
    name = ObjectProperty(None)

    def btn(self):
        x=np.arange(-4,4,0.1)
        y=np.log(x)
        plt.plot(x,y,"g",label="first line")
        plt.legend()
        plt.xlabel("x")
        plt.ylabel("y")
        plt.title("first graphic",fontsize=15)
        plt.grid(True)
        box = BoxLayout()
        box.add_widget(FigureCanvasKivyAgg(plt.gcf()))


class MyApp(App):

    def build(self):

        return Plot()

if __name__ == '__main__':
    MyApp().run()
#------------------- tab.kv

<Plot>:

    name:name

    size_hint: 1,1
    pos_hint: {'center_x': .5, 'center_y': .5}

    do_default_tab: False


    TabbedPanelItem:
        text: 'first tab'

        FloatLayout:

            Label:

                font_size:30
                halign: 'center'
                text: 'test\ntest1\ntest2'
                size_hint: 0.3,0.1
                pos_hint: {"x":0.5-0.3/2,"top":0.5+0.1/2}


    TabbedPanelItem:
        text: 'second tab'

        FloatLayout:

            Button:
                id: name
                text:"line chart"
                size_hint: 0.3,0.1
                pos_hint: {"x":0.02,"top":0.98}
                on_press:root.btn()