python - 改变python tkinter中变量的值

Question

我刚刚开始使用 python tkinter，但无法获得更改日期时间中日期的按钮。到目前为止，我有按钮更改值变量 b、c 和 d，但它不会更改日期。感谢您的帮助。

from tkinter import *
import datetime
window = Tk()
b = int(1999)
c = int(2)
d = int(2)
today = datetime.date.today()
def changeVariable():
    global b, c, d
    b = int(1914)
    print("changed b")
    c = int(7)
    print("changed c")
    d = int(28)
    print("changed d")

def printVariable():
    global a
    print(a.days)

dog = datetime.date(b, c, d)
a = today - dog
button1 = Button(window, command = changeVariable)
button1.pack()
button2 = Button(window, command = printVariable)
button2.pack()

Answer 1

您的函数 changeVariable 确实更改变量 b、c 和 d.只是在此之前计算了a。 Python 以及大多数编程语言的工作方式是，当您说 x = y 时，除非特殊情况，并不意味着:

x is equal to y at all times. (pass by reference)

而是:

put y's this very instant value to x (pass by value)

所以你应该这样写:

dog = datetime.date(b, c, d)
a = today - dog

在您的 printVariable 中，以便 a 的值也会更新。

您的最终 printVariable 应类似于:

def printVariable():
    global a
    dog = datetime.date(b, c, d)
    a = today - dog
    print(a.days)