GUI Code

from tkinter import *


class Inch_Real_Size:
    def __init__(self, inch):
        self.inch = inch

        frame= Frame(inch)
        frame.pack()
        Label(frame,text = 'Given Inch').grid(row = 0, column = 0)
        self.I_var = DoubleVar()
        Entry(frame, textvariable= self.I_var).grid(row=0,column=1)
        Label(frame, text = 'Real Size').grid(row=1,column=0)
        self.result_var=DoubleVar()
        Label(frame,textvariable=self.result_var).grid(row=1, column=1)
        button = Button(frame,text = 'Find real size', command =self.convert)
        button.grid(row=2, columnspan=2)

    def convert(inch):


        if inch <= 15:
            return inch / (2*inch)

        elif inch == 5:
            return 5 - 4

        elif inch <= 14:
            return inch * (1/3)



root = Tk()
root.wm_title('Real Size')
Size = Inch_Real_Size(root)
root.mainloop()