只打印一个单词时出现异常

Question

我有一节课是这样的：

def set_new_mode(self,mode):
    try:
        #this will fail, since self.keithley is never initialized
        print self.keithley
        self.keithley.setzerocheck(on=True)
        self.keithley.selectmode(mode,nplc=6)
        self.keithley.setzerocheck(on=False) #keithcontrol class will 
        #automatically turn on zero correction when zchk is disabled
        self.mode = mode
        self.print_to_log('\nMode set to %s' % self.mode)
    except Exception as e:
        self.print_to_log('\nERROR:set_new_mode: %s' % e)
        print e

作为一些错误处理测试的一部分，我尝试在不初始化类变量self.keithley的情况下调用set_new_mode函数。在本例中，我希望print self.keithley语句将引发AttributeError: keithgui instance has no attribute 'keithley'。但是，print e和self.print_to_log('\nERROR:set_new_mode: %s' % e)表示e只包含单词“keithley”。你知道吗

将print e更改为print type(e)会显示e仍然具有类型AttributeError，但该变量不再包含有关异常的任何有用信息。为什么？如何将e返回到预期的形式？你知道吗

编辑：这里是一个新的复制错误。要重现错误，请启动GUI，将模式更改为VOLT以外的模式，然后单击“更新”按钮。

import Tkinter

import numpy as np
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg, NavigationToolbar2TkAgg


class keithgui(Tkinter.Tk):
    def __init__(self,parent):
        Tkinter.Tk.__init__(self,parent)
        self.parent = parent
        self.initialize()

    def initialize(self):
        #we are not initially connected to the keithley
        self.connected = False
        self.pauseupdate = False

        #set up frames to distribute widgets
        #MASTER FRAME
        self.mframe = Tkinter.Frame(self,bg='green')
        self.mframe.pack(side=Tkinter.TOP,fill='both',expand=True)
        #LEFT AND RIGHT FRAMES
        self.Lframe = Tkinter.Frame(self.mframe,bg='red',borderwidth=2,relief='raised')
        self.Lframe.pack(side='left',fill='both',expand=True)
        self.Rframe = Tkinter.Frame(self.mframe,bg='blue',borderwidth=2,relief='raised')
        self.Rframe.pack(side='right',fill='both',expand=False)

        #create the log text widget to keep track of what we did last
        #also give it a scrollbar...
        scrollbar = Tkinter.Scrollbar(master=self.Lframe)
        scrollbar.pack(side=Tkinter.RIGHT,anchor='n')
        self.logtext = Tkinter.Text(master=self.Lframe,height=3,yscrollcommand=scrollbar.set)
        scrollbar.config(command=self.logtext.yview)
        self.logtext.pack(side=Tkinter.TOP,anchor='w',fill='both')

        #Button to update all settings
        updatebutton = Tkinter.Button(master=self.Rframe,text='Update',command=self.update_all_params)
        updatebutton.grid(column=2,row=0)


        #Option menu & label to select mode of the Keithley
        modes = ['VOLT','CHAR','CURR']
        modelabel = Tkinter.Label(master=self.Rframe,text='Select Mode:')
        modelabel.grid(column=0,row=2,sticky='W') 
        self.mode = 'VOLT'
        self.modevar = Tkinter.StringVar()
        self.modevar.set(self.mode)
        modeselectmenu = Tkinter.OptionMenu(self.Rframe,self.modevar,*modes)
        modeselectmenu.grid(column=1,row=2,sticky='W')

    def print_to_log(self,text,loc=Tkinter.END):
        self.logtext.insert(loc,text)
        self.logtext.see(Tkinter.END)



    def update_all_params(self):
        self.set_refresh_rate()
        if self.modevar.get() != self.mode:
            self.set_new_mode(self.modevar.get())
        else:
            self.print_to_log('\nAlready in mode %s' % self.mode)

    def set_refresh_rate(self):
        try:
            self.refreshrate = np.float(self.refreshrateentryvar.get())
            self.print_to_log('\nRefresh rate set to %06.3fs' % self.refreshrate)
        except Exception as e:
            self.print_to_log('\nERROR:set_referesh_rate: %s' % e)

    def set_new_mode(self,mode):
        try:
            print self.keithley
            self.keithley.setzerocheck(on=True)
            self.keithley.selectmode(mode,nplc=6)
            self.keithley.setzerocheck(on=False) #keithcontrol class will 
            #automatically turn on zero correction when zchk is disabled
            self.mode = mode
            self.print_to_log('\nMode set to %s' % self.mode)
        except Exception as e:
            self.print_to_log('\nERROR:set_new_mode: %s' % e)
            print e
            print type(e)

if __name__ == "__main__":
    app = keithgui(None)
    app.title('Keithley GUI')
    app.mainloop()

Answer 1

如果修改代码：

import Tkinter as tk

class Fnord(tk.Tk):
    def set_new_mode(self,mode):
        try:
            import pdb; pdb.set_trace()
            #this will fail, since self.keithley is never initialized
            print self.keithley

Fnord().set_new_mode('whatever')

然后开始使用s，您将看到在您的窗口中有一个__getattr__函数。我想看看是什么导致了这个问题，但这实际上是你的答案。你知道吗

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在调用堆栈之后，它引导我调用self.tk = _tkinter.create，最终导致我得到here。归根结底，这个异常发生在C-territory中，因此它产生了一个不同的AttributeError消息。你知道吗