tkinter点击按钮切换页面时如何仅在进入Page2时执行循环打印列表

所有页面实例在MainView初始化阶段就会被统一创建，Page2类的__init__方法会在此时执行，因此for循环逻辑会在程序启动时提前运行，而非等待切换到Page2时触发。

将需要在切换到Page2时才执行的逻辑从__init__方法迁移到父类预定义的show方法中，可按需增加初始化标记避免每次切换页面都重复执行逻辑。同时将按钮的触发逻辑统一改为调用页面对象的show方法。

import tkinter as tk

class Page(tk.Frame):
    def __init__(self, *args, **kwargs):
        tk.Frame.__init__(self, *args, **kwargs)
    def show(self):
        self.lift()

class Page1(Page):
   def __init__(self, *args, **kwargs):
       Page.__init__(self, *args, **kwargs)
       label = tk.Label(self, text="This is page 1")
       label.pack(side="top", fill="both", expand=True)

class Page2(Page):
   def __init__(self, *args, **kwargs):
       Page.__init__(self, *args, **kwargs)
       # 仅初始化label占位，逻辑执行后再更新内容
       self.label = tk.Label(self, text="")
       self.label.pack(side="top", fill="both", expand=True)
       # 初始化标记，避免逻辑重复执行
       self._initialized = False

   def show(self):
       # 仅第一次打开Page2时执行逻辑，若需要每次打开都执行可删除判断
       if not self._initialized:
           L=[]
           for x in ["A","B"]:
               print(x)
               L.append(x)
           self.label.config(text=L)
           self._initialized = True
       self.lift()

class Page3(Page):
   def __init__(self, *args, **kwargs):
       Page.__init__(self, *args, **kwargs)
       label = tk.Label(self, text="This is page 3")
       label.pack(side="top", fill="both", expand=True)

class MainView(tk.Frame):
    def __init__(self, *args, **kwargs):
        tk.Frame.__init__(self, *args, **kwargs)
        p1 = Page1(self)
        p2 = Page2(self)
        p3 = Page3(self)

        buttonframe = tk.Frame(self)
        container = tk.Frame(self)
        buttonframe.pack(side="top", fill="x", expand=False)
        container.pack(side="top", fill="both", expand=True)

        p1.place(in_=container, x=0, y=0, relwidth=1, relheight=1)
        p2.place(in_=container, x=0, y=0, relwidth=1, relheight=1)
        p3.place(in_=container, x=0, y=0, relwidth=1, relheight=1)

        # 按钮触发改为调用show方法，保持逻辑统一
        b1 = tk.Button(buttonframe, text="Page 1", command=p1.show)
        b2 = tk.Button(buttonframe, text="Page 2", command=p2.show)
        b3 = tk.Button(buttonframe, text="Page 3", command=p3.show)

        b1.pack(side="left")
        b2.pack(side="left")
        b3.pack(side="left")

        p1.show()

if __name__ == "__main__":
    root = tk.Tk()
    main = MainView(root)
    main.pack(side="top", fill="both", expand=True)
    root.wm_geometry("400x400")
    root.mainloop()

内容的提问来源于stack exchange，提问作者Stat