from tkinter import *
from tkinter import ttk

def calculate(*args):
    try:
        value = float(boxl.get())
        value2 = float(boxr.get())
        value3 = value/value2
        if value3 < 1.43:
            if value3 > 1.23:
                aspect.set("4:3")
            else:
                aspect.set("Error")
        elif value3 < 1.87:
            if value3 > 1.67:
                aspect.set("16:9")
            else:
                aspect.set("Error")
        elif value3 > 1.87:
            aspect.set("Error")
        else:
            aspect.set("Error")
    except ValueError:
        pass

root = Tk()
root.title("Aspect Ratio")

mainframe = ttk.Frame(root, padding="3 3 12 12")
mainframe.grid(column=0, row=0, sticky=(N, W, E, S))
mainframe.columnconfigure(0, weight=1)
mainframe.rowconfigure(0, weight=1)

aspect = StringVar()
boxl = StringVar()
boxr = StringVar()

feet1_entry = ttk.Entry(mainframe, width=7, textvariable=boxr)
feet1_entry.grid(column=1, row=2, sticky=(W, E))

feet_entry = ttk.Entry(mainframe, width=7, textvariable=boxl)
feet_entry.grid(column=1, row=1, sticky=(W, E))

ttk.Label(mainframe, textvariable=aspect).grid(column=2, row=3, sticky=(W, E))
ttk.Button(mainframe, text="Calculate", command=calculate).grid(column=3, row=1, sticky=W)

ttk.Label(mainframe, text="Width").grid(column=2, row=1, sticky=W)
ttk.Label(mainframe, text="Height").grid(column=2, row=2, sticky=W)
ttk.Label(mainframe, text="Aspect Ratio:").grid(column=1, row=3, sticky=W)

for child in mainframe.winfo_children(): child.grid_configure(padx=5, pady=5)

feet_entry.focus()
root.bind('<Return>', calculate)

root.mainloop()