import tkinter as tk

root = tk.Tk()  # Main box window
root.title("Standard Calculator")  # Title shown at the title bar
root.resizable(0, 0)  # disabling the resizeing of the window

# Creating an entry field:
e = tk.Entry(root,
             width=35,
             bg='#f0ffff',
             fg='black',
             borderwidth=5,
             justify='right',
             font='Calibri 15')
e.grid(row=0, column=0, columnspan=3, padx=12, pady=12)


def buttonClick(num):  # function for clicking
    temp = e.get(
    )  # temporary varibale to store the current input in the screen
    e.delete(0, tk.END)  # clearing the screen from index 0 to END
    e.insert(0, temp + num)  # inserting the incoming number input


def buttonClear():  # function for clearing
    e.delete(0, tk.END)


def buttonGet(
        oper
):  # function for storing the first input and printing '+, -, /, *'
    global num1, math  # global variable num1 and math to use in function buttonEqual()
    num1 = e.get()  # getting first number
    math = oper  # oper varaible is the type of operation being performed
    e.insert(tk.END, math)
    try:
        num1 = float(num1)  # converting the number to float type
    except ValueError:  # in case there is a character other than numerals, clear the screen
        buttonClear()


def buttonEqual():  # function for printing the sum
    inp = e.get()  # getting the inserted input
    num2 = float(inp[inp.index(math) + 1:])  # getting the second number
    e.delete(0, tk.END)
    if math == '+':  # Addition
        e.insert(0, str(num1 + num2))
    elif math == '-':  # Subtraction
        e.insert(0, str(num1 - num2))
    elif math == 'x':  # Multiplication
        e.insert(0, str(num1 * num2))
    elif math == '/':  # Division
        try:
            e.insert(0, str(num1 / num2))
        except ZeroDivisionError:
            # in case there is a zero in the denominator, answer is undefined
            e.insert(0, 'Undefined')


# Defining Buttons:
b1 = tk.Button(root,
               text='1',
               padx=40,
               pady=10,
               command=lambda: buttonClick('1'),
               font='Calibri 12')
b2 = tk.Button(root,
               text='2',
               padx=40,
               pady=10,
               command=lambda: buttonClick('2'),
               font='Calibri 12')
b3 = tk.Button(root,
               text='3',
               padx=40,
               pady=10,
               command=lambda: buttonClick('3'),
               font='Calibri 12')
b4 = tk.Button(root,
               text='4',
               padx=40,
               pady=10,
               command=lambda: buttonClick('4'),
               font='Calibri 12')
b5 = tk.Button(root,
               text='5',
               padx=40,
               pady=10,
               command=lambda: buttonClick('5'),
               font='Calibri 12')
b6 = tk.Button(root,
               text='6',
               padx=40,
               pady=10,
               command=lambda: buttonClick('6'),
               font='Calibri 12')
b7 = tk.Button(root,
               text='7',
               padx=40,
               pady=10,
               command=lambda: buttonClick('7'),
               font='Calibri 12')
b8 = tk.Button(root,
               text='8',
               padx=40,
               pady=10,
               command=lambda: buttonClick('8'),
               font='Calibri 12')
b9 = tk.Button(root,
               text='9',
               padx=40,
               pady=10,
               command=lambda: buttonClick('9'),
               font='Calibri 12')
b0 = tk.Button(root,
               text='0',
               padx=40,
               pady=10,
               command=lambda: buttonClick('0'),
               font='Calibri 12')
bdot = tk.Button(root,
                 text='.',
                 padx=41,
                 pady=10,
                 command=lambda: buttonClick('.'),
                 font='Calibri 12')

badd = tk.Button(root,
                 text='+',
                 padx=29,
                 pady=10,
                 command=lambda: buttonGet('+'),
                 font='Calibri 12')
bsub = tk.Button(root,
                 text='-',
                 padx=30,
                 pady=10,
                 command=lambda: buttonGet('-'),
                 font='Calibri 12')
bmul = tk.Button(root,
                 text='x',
                 padx=30,
                 pady=10,
                 command=lambda: buttonGet('x'),
                 font='Calibri 12')
bdiv = tk.Button(root,
                 text='/',
                 padx=30.5,
                 pady=10,
                 command=lambda: buttonGet('/'),
                 font='Calibri 12')

bclear = tk.Button(root,
                   text='AC',
                   padx=20,
                   pady=10,
                   command=buttonClear,
                   font='Calibri 12')
bequal = tk.Button(root,
                   text='=',
                   padx=39,
                   pady=10,
                   command=buttonEqual,
                   font='Calibri 12')

# Putting the buttons on the screen:
b1.grid(row=3, column=0)
b2.grid(row=3, column=1)
b3.grid(row=3, column=2)
badd.grid(row=3, column=3)

b4.grid(row=2, column=0)
b5.grid(row=2, column=1)
b6.grid(row=2, column=2)
bmul.grid(row=2, column=3)

b7.grid(row=1, column=0)
b8.grid(row=1, column=1)
b9.grid(row=1, column=2)
bdiv.grid(row=1, column=3)

b0.grid(row=4, column=0)
bdot.grid(row=4, column=1)
bequal.grid(row=4, column=2)
bsub.grid(row=4, column=3)

bclear.grid(row=0, column=3)

# Looping the window:
root.mainloop()