from tkinter import *

def send():
   str = txt.get(); print("Hello "+str)
   txt.config(state=DISABLED)
def delete():
   txt.config(state=NORMAL)
   txt.delete(0,END)

win = Tk()
txt = Entry(win,font=("Arial",50)); txt.pack(side=LEFT)

sub_button = Button(win,text="send",command=send); sub_button.pack(side=RIGHT)
del_button = Button(win,text="del",command=delete); del_button.pack(side=RIGHT)

win.mainloop()