Python Kivy: Build a standard calculator application – Buttons functionality part 2

In the previous part of this tutorial, we covered the basics of building a standard calculator application using Python Kivy. In this part, we will focus on implementing the functionality of the buttons in the calculator app.

Button functionality

To implement the functionality of the calculator buttons, we will define several functions that will handle the different operations such as addition, subtraction, multiplication, division, etc. We will also define functions to handle clearing the display and evaluating the expression.

Let’s start by creating a function for each operation:

  def add_number(self, number):
      self.expression += str(number)
      self.update_display()

  def clear(self):
      self.expression = ""
      self.update_display()

  def evaluate(self):
      try:
          self.expression = str(eval(self.expression))
          self.update_display()
      except Exception as e:
          self.expression = "Error"
          self.update_display()

Now that we have defined the functions for adding numbers, clearing the display, and evaluating the expression, we need to update the display to show the result of the operations. We can achieve this by adding the following code to the update_display function:

  def update_display(self):
      self.display.text = self.expression

Finally, we need to bind the buttons in the calculator app to the corresponding functions. This can be done by adding the following code to the Kivy file:

  Button:
    text: "1"
    on_press: root.add_number(1)

  Button:
    text: "2"
    on_press: root.add_number(2)

  Button:
    text: "+"
    on_press: root.add_number('+')

  Button:
    text: "-"
    on_press: root.add_number('-')

  Button:
    text: "C"
    on_press: root.clear()

  Button:
    text: "="
    on_press: root.evaluate()

With these changes, the calculator app now has the functionality to add numbers, perform operations, clear the display, and evaluate the expression. This completes the implementation of the button functionality in the calculator app using Python Kivy.

By following this tutorial, you can easily build a standard calculator application with the help of Python Kivy and implement the necessary button functionality to make the app fully functional.