python code to make a calculator frame

1# importing everyting from tkinter
2from tkinter import *
3# expression to access among all the functions
4expression = ""
5# functions
6def input_number(number, equation):
7   # accessing the global expression variable
8   global expression
9   # concatenation of string
10   expression = expression + str(number)
11   equation.set(expression)
12def clear_input_field(equation):
13   global expression
14   expression = ""
15   # setting empty string in the input field
16   equation.set("Enter the expression")
17def evaluate(equation):
18global expression
19# trying to evaluate the expression
20try:
21result = str(eval(expression))
22# showing the result in the input field
23equation.set(result)
24# setting expression to empty string
25expression = ""
26except:
27# some error occured
28# showing it to the user equation.set("Enter a valid expression")
29expression = ""
30# creating the GUI
31def main():
32   # main window window = Tk()
33   # setting the title of GUI window
34   window.title("Calculator")
35   # set the configuration of GUI window
36   window.geometry("325x175")
37   # varible class instantiation
38   equation = StringVar()
39   # input field for the expression
40   input_field = Entry(window, textvariable=equation)
41   input_field.place(height=100)
42   # we are using grid position
43   # for the arrangement of the widgets
44   input_field.grid(columnspan=4, ipadx=100, ipady=5)
45   # settin the placeholder message for users
46   equation.set("Enter the expression")
47   # creating buttons and placing them at respective positions
48   _1 = Button(window, text='1', fg='white', bg='black', bd=0, command=lambda: input_number(1, equation), height=2, width=7)
49   _1.grid(row=2, column=0)
50   _2 = Button(window, text='2', fg='white', bg='black', bd=0, command=lambda: input_number(2, equation), height=2, width=7)
51   _2.grid(row=2, column=1)
52   _3 = Button(window, text='3', fg='white', bg='black', bd=0, command=lambda: input_number(3, equation), height=2, width=7)
53   _3.grid(row=2, column=2)
54   _4 = Button(window, text='4', fg='white', bg='black', bd=0, command=lambda: input_number(4, equation), height=2, width=7)
55   _4.grid(row=3, column=0)
56   _5 = Button(window, text='5', fg='white', bg='black', bd=0, command=lambda: input_number(5, equation), height=2, width=7)
57   _5.grid(row=3, column=1)
58   _6 = Button(window, text='6', fg='white', bg='black', bd=0, command=lambda: input_number(6, equation), height=2, width=7)
59   _6.grid(row=3, column=2)
60   _7 = Button(window, text='7', fg='white', bg='black', bd=0, command=lambda: input_number(7, equation), height=2, width=7)
61   _7.grid(row=4, column=0)
62   _8 = Button(window, text='8', fg='white', bg='black', bd=0, command=lambda: input_number(8, equation), height=2, width=7)
63   _8.grid(row=4, column=1)
64   _9 = Button(window, text='9', fg='white', bg='black', bd=0, command=lambda: input_number(9, equation), height=2, width=7)
65   _9.grid(row=4, column=2)
66   _0 = Button(window, text='0', fg='white', bg='black', bd=0, command=lambda: input_number(0, equation), height=2, width=7)
67   _0.grid(row=5, column=0)
68   plus = Button(window, text='+', fg='white', bg='black', bd=0, command=lambda: input_number('+', equation), height=2, width=7)
69   plus.grid(row=2, column=3)
70   minus = Button(window, text='-', fg='white', bg='black', bd=0, command=lambda: input_number('-', equation), height=2, width=7)
71   minus.grid(row=3, column=3)
72   multiply = Button(window, text='*', fg='white', bg='black', bd=0, command=lambda:  input_number('*', equation), height=2, width=7)
73   multiply.grid(row=4, column=3)
74   divide = Button(window, text='/', fg='white', bg='black', bd=0, command=lambda: input_number('/', equation), height=2, width=7)
75   divide.grid(row=5, column=3)
76   equal = Button(window, text='=', fg='white', bg='black', bd=0, command=lambda: evaluate(equation), height=2, width=7)
77   equal.grid(row=5, column=2)
78   clear = Button(window, text='Clear', fg='white', bg='black', bd=0, command=lambda: clear_input_field(equation), height=2, width=7)
79   clear.grid(row=5, column=1)
80   # showing the GUI
81   window.mainloop()
82# start of the program
83if __name__ == '__main__':
84      main()
85