Tkinter Calculator

import tkinter as tk


class Calculator:
    def __init__(self, master):
        self.master = master
        master.title("Calculator")

        # create entry widget for input and display
        self.entry = tk.Entry(master, width=35, bg='black', fg='white', borderwidth=5)
        self.entry.grid(row=0, column=0, columnspan=4, padx=10, pady=10)

        # create buttons for calculator
        self.button_1 = tk.Button(master, text="1", padx=40, pady=20, command=lambda: self.button_click(1))
        self.button_2 = tk.Button(master, text="2", padx=40, pady=20, command=lambda: self.button_click(2))
        self.button_3 = tk.Button(master, text="3", padx=40, pady=20, command=lambda: self.button_click(3))
        self.button_4 = tk.Button(master, text="4", padx=40, pady=20, command=lambda: self.button_click(4))
        self.button_5 = tk.Button(master, text="5", padx=40, pady=20, command=lambda: self.button_click(5))
        self.button_6 = tk.Button(master, text="6", padx=40, pady=20, command=lambda: self.button_click(6))
        self.button_7 = tk.Button(master, text="7", padx=40, pady=20, command=lambda: self.button_click(7))
        self.button_8 = tk.Button(master, text="8", padx=40, pady=20, command=lambda: self.button_click(8))
        self.button_9 = tk.Button(master, text="9", padx=40, pady=20, command=lambda: self.button_click(9))
        self.button_0 = tk.Button(master, text="0", padx=40, pady=20, command=lambda: self.button_click(0))

        self.button_add = tk.Button(master, text="+", padx=39, pady=20, command=self.button_add)
        self.button_subtract = tk.Button(master, text="-", padx=41, pady=20, command=self.button_subtract)
        self.button_multiply = tk.Button(master, text="*", padx=40, pady=20, command=self.button_multiply)
        self.button_divide = tk.Button(master, text="/", padx=41, pady=20, command=self.button_divide)

        self.button_clear = tk.Button(master, text="Clear", padx=79, pady=20, command=self.button_clear)
        self.button_equals = tk.Button(master, text="=", padx=91, bg='green', fg='white', pady=20,
                                       command=self.button_equals)

        # put buttons on screen
        self.button_1.grid(row=3, column=0)
        self.button_2.grid(row=3, column=1)
        self.button_3.grid(row=3, column=2)

        self.button_4.grid(row=2, column=0)
        self.button_5.grid(row=2, column=1)
        self.button_6.grid(row=2, column=2)

        self.button_7.grid(row=1, column=0)
        self.button_8.grid(row=1, column=1)
        self.button_9.grid(row=1, column=2)

        self.button_0.grid(row=4, column=0)

        self.button_add.grid(row=5, column=0)
        self.button_subtract.grid(row=6, column=0)
        self.button_multiply.grid(row=6, column=1)
        self.button_divide.grid(row=6, column=2)
        self.button_clear.grid(row=4, column=1, columnspan=2)
        self.button_equals.grid(row=5, column=1, columnspan=2)

    # button click function to add digits to input field
    def button_click(self, number):
        current = self.entry.get()
        self.entry.delete(0, tk.END)
        self.entry.insert(0, str(current) + str(number))

    # math operation functions
    def button_add(self):
        first_number = self.entry.get()
        self.entry.delete(0, tk.END)
        self.first_number = float(first_number)
        self.math_operation = "+"

    def button_subtract(self):
        first_number = self.entry.get()
        self.entry.delete(0, tk.END)
        self.first_number = float(first_number)
        self.math_operation = "-"

    def button_multiply(self):
        first_number = self.entry.get()
        self.entry.delete(0, tk.END)
        self.first_number = float(first_number)
        self.math_operation = "*"

    def button_divide(self):
        first_number = self.entry.get()
        self.entry.delete(0, tk.END)
        self.first_number = float(first_number)
        self.math_operation = "/"

    # clear and equals functions
    def button_clear(self):
        self.entry.delete(0, tk.END)

    def button_equals(self):
        second_number = self.entry.get()
        self.entry.delete(0, tk.END)

        if self.math_operation == "+":
            self.entry.insert(0, self.first_number + float(second_number))

        elif self.math_operation == "-":
            self.entry.insert(0, self.first_number - float(second_number))

        elif self.math_operation == "*":
            self.entry.insert(0, self.first_number * float(second_number))

        elif self.math_operation == "/":
            if float(second_number) == 0:
                self.entry.delete(0, tk.END)
                self.entry.insert(0, "Error division by zero")
                return
            self.entry.insert(0, self.first_number / float(second_number))


root = tk.Tk()
calculator = Calculator(root)
root.mainloop()