TypeError: 'NoneType' object does not support item assignment

Question

def handleEnterEvent(event):     label1['text'] = "You enter the frame"     label2['text'] = ""     label3['text'] = "Sichuan University of Science and Engineering"label1 = tkinter.Label(frame1, text="No event happened", foreground="#0000ff", background="#00ff00").place(x=16, y=20) File "/Users/2020yang/Desktop/Python/Python_Basic/excise/GUI/ex1/tkinter_key.py", line 11, in handleLeaveEvent    label1['text'] = "You leave the frame"TypeError: 'NoneType' object does not support item assignment