from tkinter import *
main = Tk()
main.geometry("360x120")

#Function

def test():
    if variablecm.get() == OPTIONS1[0]:
        cm = int(num1.get()) * 10
        return cm
    if variablecm.get() == OPTIONS1[1]:
        cm = int(num1.get()) * 2.54
        return cm
    if variablecm.get() == OPTIONS1[2]:
        cm = int(num1.get()) / 10
        return cm



def test1 ():
    if variable.get() == OPTIONS2[0]:
        ans = int(test()) / 10
        num2.delete(0, END)
        num2.insert(0, ans)
    if variable.get() == OPTIONS2[1]:
        ans = int(test()) / 2.54
        num2.delete(0, END)
        num2.insert(0, ans)
    if variable.get() == OPTIONS2[2]:
        ans = int(test()) * 10
        num2.delete(0, END)
        num2.insert(0, ans)



#Entry
num1 = Entry(main)
num1.grid(row=0, column=0)

num2 = Entry(main)
num2.grid(row=1, column=0)

#options

OPTIONS1 = [
    "decimeter",
    "inches",
    "millimeter",
]


OPTIONS2 = [
    "decimeter",
    "inches",
    "millimeter",
]

#Variable
variable = StringVar(main)
variable.set(OPTIONS2[0])

variablecm = StringVar(main)
variablecm.set(OPTIONS1[0])


w2 = OptionMenu(main, variablecm, OPTIONS1[0], OPTIONS1[1], OPTIONS1[2])
w2.grid(row=0, column=1)

w1 = OptionMenu(main, variable, OPTIONS2[0], OPTIONS2[1], OPTIONS2[2])
w1.grid(row=1, column=1)


#Button
Button(text="Calculate", command=test1).grid(row=3, column=1)


main.mainloop()