python怎么把entry1输入框的内容读取放到entry3输入框中

可参考下列代码实现：

from tkinter import *

def submit():
    p.set(u.get())

root = Tk()
root.title("测试")
frame = Frame(root)
frame.pack(padx=8, pady=8, ipadx=4)

u = StringVar()
ent1 = Entry(frame, textvariable=u)
ent1.grid(row=0, column=1, sticky='ew', columnspan=2)

p = StringVar()
ent2 = Entry(frame, textvariable=p)
ent2.grid(row=1, column=1, sticky='ew', columnspan=2)

button = Button(frame, text="confirm", command=submit, default='active')
button.grid(row=2, column=1)

root.mainloop()