Python AttributeError实例没有属性

Question

我得到了以下错误：-

AttributeError: PageOne instance has no attribute 'scann'

我正在尝试运行bash脚本(run聚焦)。还是找不出我为什么会犯这个错误。我的代码如下：

class PageOne(tk.Frame):

    def __init__(self, parent, controller):

        running = False  # Global flag

        tk.Frame.__init__(self, parent)
        self.controller = controller

        button = tk.Button(self, text="Go to the start page",
                           command=lambda: controller.show_frame("StartPage"))
        strt = tk.Button(self, text="Start Scan", command=self.start)
        stp = tk.Button(self, text="Stop", command=self.stop)

        button.pack()       
        strt.pack()
        stp.pack()
        self.after(1000, self.scann)  # After 1 second, call scanning

    def scann(self):
        if running:
          sub.call(['./runfocus'], shell=True)

        self.after(1000, self.scann)

    def start(self):
        """Enable scanning by setting the global flag to True."""
        global running
        running = True

    def stop(self):
        """Stop scanning by setting the global flag to False."""
        global running
        running = False

请提供你的宝贵建议。

Answer 1

我无法复制AttributeError: PageOne instance has no attribute 'scann' error，但是由于running标志，您的脚本还有其他问题。您应该避免使用可修改的全局值，并且当您已经拥有一个类时，绝对没有必要使用单独的全局。只需创建一个属性作为标志。

下面是一个可运行的修复版本的代码。我将sub.call(['./runfocus'], shell=True)调用替换为一个简单的print调用，这样我们就可以看到start和stop的行为是正确的。

import tkinter as tk

class PageOne(tk.Frame):
    def __init__(self, parent, controller):
        self.running = False

        tk.Frame.__init__(self, parent)
        self.controller = controller

        button = tk.Button(self, text="Go to the start page",
                           command=lambda: controller.show_frame("StartPage"))
        strt = tk.Button(self, text="Start Scan", command=self.start)
        stp = tk.Button(self, text="Stop", command=self.stop)

        button.pack()
        strt.pack()
        stp.pack()
        self.after(1000, self.scann)  # After 1 second, call scanning

    def scann(self):
        if self.running:
            #sub.call(['./runfocus'], shell=True)
            print("calling runfocus")

        self.after(1000, self.scann)

    def start(self):
        """Enable scanning by setting the flag to True."""
        self.running = True

    def stop(self):
        """Stop scanning by setting the flag to False."""
        self.running = False


root = tk.Tk()
frame = PageOne(root, root)
frame.pack()
root.mainloop()