执行按钮时如何将焦点设置回原始条目小部件？（Python）

我是 Python 和 tkinter 的新手...

当按下“btn_add”时，我一直试图将焦点设置回“itemnum”。但是它不起作用......之后焦点将停留在“lotnum”条目小部件上。

我尝试使用绑定到事件''来创建一个新函数 def FocusSet

但仍然无法正常工作。我想我在这一点上有传递参数的问题..

有人可以指出我正确的方向吗？非常感谢。谢谢！

以下是脚本：

from tkinter import *
import tkinter.messagebox as tkMessageBox
import tkinter.ttk as ttk

ShowAddNew = Tk()


ITEM_NUM = StringVar()
LOT_NUM = StringVar()
UM = StringVar()

def ShowAddNew():
    global addnewform
    addnewform = Toplevel()
    addnewform.title("Mock Count/Add new")
    width = 230
    height = 260
    addnewform.geometry("%dx%d+%d+%d" % (width, height, 0, 0))
    addnewform.resizable(0, 0)
    AddNewForm()

def AddNewForm():
    TopAddNew = Frame(addnewform, width=220, height=10, bd=1, relief=SOLID)
    TopAddNew.pack(side=TOP, pady=5)
    lbl_text = Label(TopAddNew, text=("Adding Count Result"), font=('arial', 9), width=220)
    lbl_text.pack(fill=X)
    MidAddNew = Frame(addnewform, width=220)
    MidAddNew.pack(side=TOP, pady=5)
    lbl_itemnum = Label(MidAddNew, text="Item Number:", font=('arial', 12), bd=6)
    lbl_itemnum.grid(row=0, sticky=W)
    lbl_lotnum = Label(MidAddNew, text="Lot:", font=('arial', 12), bd=6)
    lbl_lotnum.grid(row=1, sticky=W)
    lbl_UoM = Label(MidAddNew, text="U of M:", font=('arial', 12), bd=6)
    lbl_UoM.grid(row=3, sticky=W)
    itemnum = Entry(MidAddNew, textvariable=ITEM_NUM, font=('arial', 10), width=20)
    itemnum.grid(row=0, column=1)
    lotnum = Entry(MidAddNew, textvariable=LOT_NUM, font=('arial', 10), width=20)
    lotnum.grid(row=1, column=1)
    UoM = OptionMenu(MidAddNew,UM,"lb","kg","case","pk","unit")
    UoM.grid(row=3, column=1)
    btn_add = Button(MidAddNew, text="Save", font=('arial', 12), width=15, bg="#009ACD", command=AddNew)
    btn_add.grid(row=4, columnspan=2, pady=5)
    btn_add.bind('<Button-1>', lambda: FocusSet(itemnum))
    ITEM_NUM.trace('w', my_tracer)

    itemnum.focus_set()

    #UM.set("(Please Select)")
    TopAddNew.mainloop()  

def my_tracer(a,b,c):
        UM.set("loading...")


def FocusSet(event):
   itemnum.focus_set()


def AddNew():
    ITEM_NUM.set("")
    LOT_NUM.set("")
    UM.set("loading...")



ShowAddNew()

if __name__ == '__main__':
    root.mainloop()

杨柳