How to add line cleaning to the calculator? Python, framework kivy?

Question

Python

How to add an AC button, as happens in calculators to clear the line?

from kivy.app import App

from kivy.uix.button import Button
from kivy.uix.widget import Widget
from kivy.uix.label import Label
from kivy.uix.gridlayout import GridLayout
from kivy.uix.boxlayout import BoxLayout

from kivy.config import Config
Config.set('graphics', 'resizable', 0)
Config.set('graphics', 'width', 350)
Config.set('graphics', 'height', 500)

class CalculatorApp(App):
  def update_label(self):
    self.lbl.text = self.formula

  def clear(instance, self):
    self.formula = 0

  def add_number(self, instance):
    if( self.formula == "0" ):
      self.formula = ""
      
    self.formula += str(instance.text)
    self.update_label()

  def add_operation(self, instance):
    self.formula += str(instance.text)
    self.update_label()

  def calc_result(self, instance):
    self.lbl.text = str(eval(self.lbl.text))
    self.formula = "0"

  def build(self):
    self.formula = "0"

    bl = BoxLayout(orientation = 'vertical', padding=10)
    gl = GridLayout(cols = 4, spacing=3, size_hint = (1, .6))

    self.lbl = Label(text="0", font_size=40, halign="right", valign="center", size_hint=(1, .4), text_size=(375 - 50, 500 * .4 - 75))
    bl.add_widget( self.lbl )

    gl.add_widget( Button(text="7", font_size=18, on_press = self.add_number) )
    gl.add_widget( Button(text="8", font_size=18, on_press = self.add_number) )
    gl.add_widget( Button(text="9", font_size=18, on_press = self.add_number) )
    gl.add_widget( Button(text="*", font_size=18, on_press = self.add_operation) )

    gl.add_widget( Button(text="4", font_size=18, on_press = self.add_number) )
    gl.add_widget( Button(text="5", font_size=18, on_press = self.add_number) )
    gl.add_widget( Button(text="6", font_size=18, on_press = self.add_number) )
    gl.add_widget( Button(text="-", font_size=18, on_press = self.add_operation) )

    gl.add_widget( Button(text="1", font_size=18, on_press = self.add_number) )
    gl.add_widget( Button(text="2", font_size=18, on_press = self.add_number) )
    gl.add_widget( Button(text="3", font_size=18, on_press = self.add_number) )
    gl.add_widget( Button(text="+", font_size=18, on_press = self.add_operation) )

    gl.add_widget( Button(text="/", font_size=18, on_press = self.add_operation) )
    gl.add_widget( Button(text="0", font_size=18, on_press = self.add_number) )
    gl.add_widget( Button(text=".", font_size=18, on_press = self.add_number) )
    gl.add_widget( Button(text="=", font_size=18, on_press = self.calc_result) )

    bl.add_widget( gl )
    return bl

if __name__ == "__main__":
  CalculatorApp().run()

Answer 1

gl.add_widget( Button(text="AC", font_size=18, on_press=self.clear) )

, may be?