Tkinter with openweather

I tried creating a dropdown box in Tkinter. I was hoping that everytime i selected a country and click onto the left button, it'll display the weather of the country that I have selected. Apparently, I have to manually change this line of code(in the define weather function) weather_status = output['list'][2]['sys']
every time i want to get the country's weather. How do I get the country's weathers without having to change that line of code manually?

import requests
import tkinter as tk 
from tkinter import Tk, BOTH, Menu, StringVar, messagebox, Label

def weather(): 
    city = city_list.get()
    url = 'http://api.openweathermap.org/data/2.5/group?id=1880252,524901,703448,2643743&units=metric&appid=de9880142c6480331da965bf187a4b6e'.format(city)
    req = requests.get(url)
    output = req.json()
    weather_status = output['list'][2]['sys']
    weather_status_label.configure(text = 'weather status: ' + str(weather_status))
    
window = tk.Tk() 
window.geometry('400x350') 

## adding a drop box
OptionList= [
             'Singapore', 
             'London', 
             'Bangkok',
             'Moscow' 
             ]
city_list = StringVar(window, OptionList)
city_list.set('select the city')
opt = tk.OptionMenu(window, city_list, *OptionList)
opt.config(width = 90, font = ('Arial', 12))
opt.pack()

## adding a label on top
lbl = tk.Label(window, text = 'Select your city', bg = 'light green')
lbl.pack()

## adding buttons
def win_quit():
    if messagebox.askokcancel('quit','Do you want to quit?'):
        window.destroy()

button_1 = tk.Button(window, text = 'Quit', height = 2, 
                     width = 4, command = win_quit, activeforeground = 'red',
                     relief = 'ridge')
button_1.place(x= 300, y= 60)

button_2 = tk.Button(window, text = 'Click', height = 2, 
                     width = 4, command = weather, activeforeground = 'green',
                     relief = 'ridge')
button_2.place(x= 70, y= 60)

## adding another label 

weather_status_label = Label(window, font=('Arial', 10,'bold' ))
weather_status_label.pack(padx= 10, pady= 60)

window.mainloop()

If I have understood your question, you can do it by "tracing" changes to the StringVar named city_list and having it call the weather() function everytime its value is changed.

Tracing is described in the document The Variable Classes (BooleanVar, DoubleVar, IntVar, StringVar).

To make it so you don't have to change the weather_status = output['list'][2]['sys'] statement in the weather() function, you can just make it reference the current city value you already have:

def weather():
city = city_list.get()
url = 'http://api.openweathermap.org/data/2.5/group?id=1880252,524901,703448,2643743&units=metric&appid=de9880142c6480331da965bf187a4b6e'.format(city)
req = requests.get(url)
output = req.json()
#    weather_status = output['list'][2]['sys']  # CHANGED.
weather_status = city
weather_status_label.configure(text = 'weather status: ' + str(weather_status))

And then add the code to do the tracing by calling this modified version of it:

...
## adding a drop box
OptionList= [
'Singapore',
'London',
'Bangkok',
'Moscow'
]
city_list = StringVar(window, OptionList)
city_list.set('select the city')
observer = city_list.trace('w', lambda *_: weather())  # ADDED.
opt = tk.OptionMenu(window, city_list, *OptionList)
opt.config(width = 90, font = ('Arial', 12))
opt.pack()
...