tkinter_app4.py

def caps_from(event):
    """Forces the input FROM to be upper case and less than 4 characters"""
    from_city1.set(from_city1.get().upper())
    if len(from_city1.get()) > 3: from_city1.set(from_city1.get()[:3])

def caps_to(event):
    """Forces the input TO to be upper case and less than 4 characters"""
    to_city1.set(to_city1.get().upper())
    if len(to_city1.get()) > 3: to_city1.set(to_city1.get()[:3])
    
def close_app():
    window.destroy()

def run_app():
    print('run')