Calculator Addition Function – Python Kivy GUI Tutorial #16

In this video we’ll build out the addition functionality of our calculator with Kivy and Python.

In the last video, we built out the basic gui for our calculator app. In this video we’ll add in some functionality.

First, we’ll write code to deal with pressing number buttons and entering them into the text box at the top of our calculator.
Then we’ll work on the math buttons (plus, minus, multiplication, and division).

After that we’ll start to work on the equal button, but only for addition.

Python Code: calc.py
GitHub Code: calc.py

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.properties import ObjectProperty
from kivy.lang import Builder
from kivy.core.window import Window

# Set the app size
Window.size = (500,700)

# Designate Our .kv design file 
Builder.load_file('calc.kv')

class MyLayout(Widget):
	def clear(self):
		self.ids.calc_input.text = '0'

	# Create a button pressing function
	def button_press(self, button):
		# create a variable that contains whatever was in the text box already
		prior = self.ids.calc_input.text
		
		# determine if 0 is sitting there
		if prior == "0":
				self.ids.calc_input.text = ''
				self.ids.calc_input.text = f'{button}'
		else: 
			self.ids.calc_input.text = f'{prior}{button}'

	# create addition function
	def add(self):
		# create a variable that contains whatever was in the text box already
		prior = self.ids.calc_input.text
		
		# slap a plus sign to the text box
		self.ids.calc_input.text = f'{prior}+'

	# create addition function
	def subtract(self):
		# create a variable that contains whatever was in the text box already
		prior = self.ids.calc_input.text
		
		# slap a plus sign to the text box
		self.ids.calc_input.text = f'{prior}-'

	# create addition function
	def multiply(self):
		# create a variable that contains whatever was in the text box already
		prior = self.ids.calc_input.text
		
		# slap a plus sign to the text box
		self.ids.calc_input.text = f'{prior}*'

	# create addition function
	def divide(self):
		# create a variable that contains whatever was in the text box already
		prior = self.ids.calc_input.text
		
		# slap a plus sign to the text box
		self.ids.calc_input.text = f'{prior}/'

	# create equals to function
	def equals(self):
		prior = self.ids.calc_input.text

		# Addition
		if "+" in prior:
			num_list = prior.split("+")
			answer = 0
			# loop thru our list
			for number in num_list:
				answer = answer + int(number)

			# print the answer in the text box
			self.ids.calc_input.text = str(answer)


class CalculatorApp(App):
	def build(self):
		return MyLayout()

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

Kivy Design Code: calc.kv
GitHub Code: calc.kv

<MyLayout>
	BoxLayout:
		orientation: "vertical"
		size: root.width, root.height
		
		TextInput:
			id: calc_input
			text: "0"
			halign: "right"
			font_size: 65
			size_hint: (1, .15)

		GridLayout:
			cols: 4
			rows: 5

			# Row
			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "%"

			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "CE"

			Button:
				id: clear
				size_hint: (.2, .2)
				font_size: 32
				text: "C"
				on_press: root.clear()
				
			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "/"
				on_press: root.divide()

			# Row
			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "7"
				background_color: (157/255, 157/255, 157/255, 1)
				on_press: root.button_press(7)

			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "8"
				background_color: (157/255, 157/255, 157/255, 1)
				on_press: root.button_press(8)

			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "9"
				background_color: (157/255, 157/255, 157/255, 1)
				on_press: root.button_press(9)

			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "x"
				on_press: root.multiply()

			# Row
			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "4"
				background_color: (157/255, 157/255, 157/255, 1)
				on_press: root.button_press(4)

			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "5"
				background_color: (157/255, 157/255, 157/255, 1)
				on_press: root.button_press(5)

			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "6"
				background_color: (157/255, 157/255, 157/255, 1)
				on_press: root.button_press(6)

			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "-"
				on_press: root.subtract()

			# Row
			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "1"
				background_color: (157/255, 157/255, 157/255, 1)
				on_press: root.button_press(1)

			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "2"
				background_color: (157/255, 157/255, 157/255, 1)
				on_press: root.button_press(2)

			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "3"
				background_color: (157/255, 157/255, 157/255, 1)
				on_press: root.button_press(3)

			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "+"
				on_press: root.add()

			# Row
			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "+/-"
				background_color: (157/255, 157/255, 157/255, 1)

			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "0"
				background_color: (157/255, 157/255, 157/255, 1)
				on_press: root.button_press(0)

			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "."
				background_color: (157/255, 157/255, 157/255, 1)


			Button:
				size_hint: (.2, .2)
				font_size: 32
				text: "="
				on_press: root.equals()