Calculator

This basic calculator demonstrates how to use color styles to differentiate button functions. The overall theme is flatly and the following styles are applied to the widgets:

Digits

primary.TButton

Operators

secondary.TButton

Equals

success.TButton

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"""
    Author: Israel Dryer
    Modified: 2021-04-09
"""
import tkinter
from tkinter import ttk

from ttkbootstrap import Style


class Application(tkinter.Tk):

    def __init__(self):
        super().__init__()
        self.title('Calculator')
        self.style = Style('flatly')
        self.style.configure('.', font='TkFixedFont 16')
        self.calc = Calculator(self)
        self.calc.pack(fill='both', expand='yes')


class Calculator(ttk.Frame):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.configure(padding=1)

        # number display
        self.display_var = tkinter.StringVar(value=0)
        self.display = ttk.Label(self, textvariable=self.display_var, font='TkFixedFont 20', anchor='e')
        self.display.grid(row=0, column=0, columnspan=4, sticky='ew', pady=15, padx=10)

        # button layout
        button_matrix = [
            ('%', 'C', 'CE', '/'), (7, 8, 9, '*'), (4, 5, 6, '-'), (1, 2, 3, '+'), ('±', 0, '.', '=')]

        # create buttons with various styling
        for i, row in enumerate(button_matrix):
            for j, lbl in enumerate(row):
                if isinstance(lbl, int):
                    btn = ttk.Button(self, text=lbl, width=2, style='primary.TButton')
                elif lbl == '=':
                    btn = ttk.Button(self, text=lbl, width=2, style='success.TButton')
                else:
                    btn = ttk.Button(self, text=lbl, width=2, style='secondary.TButton')
                btn.grid(row=i + 1, column=j, sticky='nsew', padx=1, pady=1, ipadx=10, ipady=10)

                # bind button press
                btn.bind("<Button-1>", self.press_button)

        # variables used for collecting button input
        self.position_left = ''
        self.position_right = '0'
        self.position_is_left = True
        self.running_total = 0.0

    def press_button(self, event):
        value = event.widget['text']

        if isinstance(value, int):
            if self.position_is_left:
                self.position_left = f'{self.position_left}{value}'
            else:
                self.position_right = str(value) if self.position_right == '0' else f'{self.position_right}{value}'
        elif value == '.':
            self.position_is_left = False
        elif value in ['/', '-', '+', '*']:
            self.operator = value
            self.running_total = float(self.display_var.get())
            self.reset_variables()
        elif value == '=':
            operation = f'{self.running_total}{self.operator}{self.display_var.get()}'
            result = eval(operation)
            self.display_var.set(result)
            return
        elif value in ['CE', 'C']:
            self.reset_variables()
            self.operator = None
            self.running_total = 0
            return

        # update the number display
        self.display_var.set('.'.join([self.position_left, self.position_right]))

    def reset_variables(self):
        self.display_var.set(0)
        self.position_is_left = True
        self.position_left = ''
        self.position_right = '0'


if __name__ == '__main__':
    Application().mainloop()