import tkinter as tk
from functools import partial

# global variable
val = "cm"

val1 = "cm"


# getting drop down value
def store_l(sel_l):
    global val
    val = sel_l

# getting drop down value
def store_l1(sel_l):
    global val1
    val1 = sel_l


# the main conversion
def call_convert(rlabel1, rlabe12, inputn, inputn1):
    l = inputn.get()
    l1 = inputn1.get()
    if val == 'cm':
        m = float(l)+float(l1)
        i = float(l)-float(l1)
        rlabel1.config(text="%f add" % m)
        rlabe12.config(text="%f sub" % i)
    # if val == 'mm':
    #     c = float(l+l1)/10
    #     i = c*0.393701
    #     rlabel1.config(text="%f cm" % c)
    #     rlabe12.config(text="%f inches" % i)
    # if val == 'inches':
    #     c = float(l+l1)/0.393701
    #     m = c*10
    #     rlabel1.config(text="%f cm" % c)
    #     rlabe12.config(text="%f mm" % m)
    return


# app window configuration and UI
root = tk.Tk()
root.geometry('400x250+100+200')
root.title('Length Converter')
root.resizable(width=False, height=False)
root.grid_columnconfigure(1, weight=1)
root.grid_rowconfigure(4, weight=1)

numberInput = tk.StringVar()
var = tk.StringVar()

numberInput1 = tk.StringVar()
var1 = tk.StringVar()

# label and entry field
input_label = tk.Label(root, text="Enter length1")
input_entry = tk.Entry(root, textvariable=numberInput)
input_label.grid(row=1)
input_entry.grid(row=1, column=1)

# label and entry field
input_label = tk.Label(root, text="Enter length 2")
input_entry = tk.Entry(root, textvariable=numberInput1)
input_label.grid(row=2)
input_entry.grid(row=2, column=1)

# result label's for showing the other two tresults
result_label1 = tk.Label(root)
result_label1.grid(row=3, columnspan=4)
result_label2 = tk.Label(root)
result_label2.grid(row=4, columnspan=4)

# drop down initalization and setup
dropDownList = ["cm", "mm", "inches"]
dropdown = tk.OptionMenu(root, var, *dropDownList, command=store_l)
var.set(dropDownList[0])
dropdown.grid(row=1, column=3)

# drop down initalization and setup
dropDownList = ["cm", "mm", "inches"]
dropdown1 = tk.OptionMenu(root, var1, *dropDownList, command=store_l)
var1.set(dropDownList[0])
dropdown1.grid(row=2, column=3)

# button click
call_convert = partial(call_convert, result_label1, result_label2, numberInput, numberInput1)
result_button = tk.Button(root, text="Convert", command=call_convert)
result_button.grid(row=6, columnspan=4)

root.mainloop()