from tkinter import *
window = Tk()
label = Label(window, text="Press F1")
label.config(font="Helvetica 14 bold")
label.pack(fill=X)
entry = Entry().pack(side=LEFT)

my_str = StringVar()

def click_F1(event):
    my_str.set('hello world')

entry = Entry(window, textvariable=my_str, state=DISABLED, width=50, bg='beige')
entry.config(font="SansSerif 16 bold")
entry.pack(fill=X)
entry.bind_all("<F1>", click_F1)
window.mainloop()