Python Kivy: Build a standard calculator application – Project Demo

Are you interested in learning how to build a standard calculator application using Python Kivy? Look no further! In this project demo, I will walk you through the process of creating a simple calculator application with a user-friendly interface using Python Kivy.

Prerequisites

Before we get started, make sure you have Python and Kivy installed on your computer. You can download and install Python from the official website (https://www.python.org/) and Kivy can be installed using pip:

		
			pip install kivy
		
	

Building the Calculator Interface

To build the calculator interface, we will use the Kivy language which is a powerful language for creating user interfaces. Here is a simple example of a Kivy language code that defines the layout of the calculator interface:

		
<GridLayout>
    <TextInput id="input" />

    <Button text="1" on_press="app.update_input(1)" />
    <Button text="2" on_press="app.update_input(2)" />
    <Button text="3" on_press="app.update_input(3)" />
    <Button text="+" on_press="app.update_input('+')" />

    <Button text="4" on_press="app.update_input(4)" />
    <Button text="5" on_press="app.update_input(5)" />
    <Button text="6" on_press="app.update_input(6)" />
    <Button text="-" on_press="app.update_input('-')" />

    <Button text="7" on_press="app.update_input(7)" />
    <Button text="8" on_press="app.update_input(8)" />
    <Button text="9" on_press="app.update_input(9)" />
    <Button text="*" on_press="app.update_input('*')" />

    <Button text="C" on_press="app.clear_input()" />
    <Button text="0" on_press="app.update_input(0)" />
    <Button text="." on_press="app.update_input('.')" />
    <Button text="/" on_press="app.update_input('/')" />

    <Button text="=" on_press="app.calculate()" />
</GridLayout>
		
	

In the above code, we define a GridLayout with TextInput for input and 16 Buttons for numbers, operators, clear button, decimal point, and equals button. We also define the actions to be taken when each button is pressed.

Implementing the Calculator Logic

Now that we have the interface ready, let’s implement the logic for the calculator. We will create a Python class that will handle the input updates and perform the calculations.

		
class CalculatorApp(App):
    def build(self):
        self.expression = ''
        return Builder.load_string(KV)

    def update_input(self, value):
        self.expression += str(value)
        self.root.ids.input.text = self.expression

    def clear_input(self):
        self.expression = ''
        self.root.ids.input.text = self.expression

    def calculate(self):
        try:
            self.expression = str(eval(self.expression))
            self.root.ids.input.text = self.expression
        except:
            self.root.ids.input.text = 'Error'

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

In the above Python code, we define a CalculatorApp class that handles the building of the calculator interface, updating the input, clearing the input, and performing the calculations.

Conclusion

That’s it! With the combination of the Kivy language and Python, we have successfully built a standard calculator application with a user-friendly interface. You can further enhance this application by adding more advanced features such as scientific functions, history log, and themes.