Python tkinter Button回调函数中已定义的变量，再使用该变量时提示未定义变量。

Question

from tkinter import Tk, Frame, Button, Label, Entry, StringVar, IntVar , mainloop
import datetime 
root = Tk()

v1 = StringVar()
v2 = StringVar()
v3 = StringVar()
v4 = int()
v5 = int()
v6 = int()


frame1 = Frame(root)
frame2 = Frame(root)
frame3 = Frame(root)
frame1.pack(padx = 20, pady = 20)
frame2.pack(padx = 20, pady = 20)
frame3.pack(padx = 20, pady = 20)

Label(frame1, text = "开始时间：").grid(row = 0, column = 0)
Entry(frame1, width = 6, textvariable = v1, validate = "key").grid(row = 0, column = 1)
Label(frame1, text = "年").grid(row = 0, column = 2)
Entry(frame1, width = 6, textvariable = v2, validate = "key").grid(row = 0, column = 3)
Label(frame1, text = "月").grid(row = 0, column = 4)
Entry(frame1, width = 6, textvariable = v3, validate = "key").grid(row = 0, column = 5)
Label(frame1, text = "日").grid(row = 0, column = 6)


def callbackMin():
    v4 = int(v1.get())
    v5 = int(v2.get())
    v6 = int(v3.get())
    Startday = datetime.date(v4, v5, v6)

theButtonMin = Button(frame1, text = "获取时间", command = callbackMin).grid(row = 0, column = 7)
frame3.bind("<Button>", callbackMin)

print(Startday)

mainloop()

目的是触发按钮时在回调函数中为变量赋值，变量在后续代码中使用。
通过Button组件回调函数获取文本框中输入的年月日时间，将获取到的时间赋值给变量Startday，后续程序使用这两个变量进行计算。
但程序运行未打开tkinter窗口，没法通过Button触发获取文本框内容，也就没法为变量Startday赋值。但程序后续代码，需要这个变量参与计算，这时会提示变量未定义(Undefined name ‘Startday’)。
尝试过为Startday定义全局变量，或在callbackSetMin()中return出这个变量值，或初始化变量，都失败了。
救助大家有啥办法。

Answer 1

你在函数里边定义的Startday是局部变量，只有在函数里边可见，应该定义为全局变量才行，可采用如下的定义方式：

from tkinter import Tk, Frame, Button, Label, Entry, StringVar, IntVar , mainloop
import datetime 
root = Tk()

v1 = StringVar()
v2 = StringVar()
v3 = StringVar()
v4 = int()
v5 = int()
v6 = int()
Startday=None


frame1 = Frame(root)
frame2 = Frame(root)
frame3 = Frame(root)
frame1.pack(padx = 20, pady = 20)
frame2.pack(padx = 20, pady = 20)
frame3.pack(padx = 20, pady = 20)

Label(frame1, text = "开始时间：").grid(row = 0, column = 0)
Entry(frame1, width = 6, textvariable = v1, validate = "key").grid(row = 0, column = 1)
Label(frame1, text = "年").grid(row = 0, column = 2)
Entry(frame1, width = 6, textvariable = v2, validate = "key").grid(row = 0, column = 3)
Label(frame1, text = "月").grid(row = 0, column = 4)
Entry(frame1, width = 6, textvariable = v3, validate = "key").grid(row = 0, column = 5)
Label(frame1, text = "日").grid(row = 0, column = 6)


def callbackMin():
    global  Startday
    v4 = int(v1.get())
    v5 = int(v2.get())
    v6 = int(v3.get())
    Startday = datetime.date(v4, v5, v6)
    print(Startday)

theButtonMin = Button(frame1, text = "获取时间", command = callbackMin).grid(row = 0, column = 7)
frame3.bind("<Button>", callbackMin)



mainloop()