温度转换器GUI UnboundLocalError/AttributeError问题

Question

我使用Tkinter在Python中制作了一个相对简单的温度应用程序。

我设法让大多数零件都能正常工作，但实际处理得到答案的部分给了我麻烦。我认为这与我决定如何从“x温度单位”转换为“y温度单位”的方式有关，通过使用if/elif将我的程序指向适当的转换函数。用我目前的尝试，我倾向于得到UnboundLocalError，据我的理解，这意味着我以某种方式试图在我为其分配任何东西之前使用变量，在这种情况下为converted_temp。但是，我不知道如何解决这个问题，因为我已经尝试将它分配给某个占位符，并且最终不会输出任何内容。有没有办法通过我编写程序的方式来解决这个错误？

这里是我写的：

import tkinter 
import tkinter.messagebox 

class TempConverterGUI: 
    def __init__(self): 
# create main window, and set a custom window title 
     self.main_window = tkinter.Tk() 
     self.main_window.wm_title("Convert Temperatures") 

# creates a top frame with label to give a title for the application 
     self.top_frame = tkinter.Frame(self.main_window) 
     self.title_label = tkinter.Label(self.top_frame, text= 'Temperature Converter') 
     self.title_label.pack(side='top') 
     self.top_frame.pack() 
# create middle frame to hold main program components 
     self.mid_frame = tkinter.Frame(self.main_window) 
############################################################################################# 
# create frame to hold the unit lists 
     self.lists_frame = tkinter.Frame(self.mid_frame) 
     ########################## 
# create frame to hold original unit to convert from list components   
     self.from_list_frame = tkinter.Frame(self.lists_frame) 
     self.from_label = tkinter.Label(self.from_list_frame, text='Convert from:') 
     self.from_label.pack(side='top') 

# creates radio button lists to allow user to decide which units to convert from 
     self.from_radio = tkinter.StringVar() 
     self.fb1 = tkinter.Radiobutton(self.from_list_frame, text= 'Fahrenheit', variable= self.from_radio, value= 'FAHRENHEIT') 
     self.fb2 = tkinter.Radiobutton(self.from_list_frame, text= 'Celsius', variable= self.from_radio, value= 'CELSIUS') 
     self.fb3 = tkinter.Radiobutton(self.from_list_frame, text= 'Kelvin', variable= self.from_radio, value= 'KELVIN') 
     self.fb1.pack() 
     self.fb2.pack() 
     self.fb3.pack() 
     ######################## 
# create frame to hold list components to decide which unit to convert to  
     self.to_list_frame = tkinter.Frame(self.lists_frame) 
     self.to_label = tkinter.Label(self.to_list_frame, text='Convert to:') 
     self.to_label.pack(side='top') 
# creates radio button lists to allow user to decide which units to convert to 
     self.to_radio = tkinter.StringVar() 
     self.tb1 = tkinter.Radiobutton(self.to_list_frame, text= 'Fahrenheit', variable= self.to_radio, value= 'FAHRENHEIT') 
     self.tb2 = tkinter.Radiobutton(self.to_list_frame, text= 'Celsius', variable= self.to_radio, value= 'CELSIUS') 
     self.tb3 = tkinter.Radiobutton(self.to_list_frame, text= 'Kelvin', variable= self.to_radio, value= 'KELVIN') 
     self.tb1.pack() 
     self.tb2.pack() 
     self.tb3.pack() 
#############################################################################################  
#Create frame to hold textbox input 
     self.entry_frame = tkinter.Frame(self.mid_frame) 


     self.temp_prompt_label = tkinter.Label(self.entry_frame, text='Enter a temperature:') 
     self.temp_entry = tkinter.Entry(self.entry_frame, width=10) 
     self.temp_prompt_label.pack(side='top') 
     self.temp_entry.pack(side='top') 
############################################################################################################################################################################ 
############################################################################################################################################################################      
# create frame to hold convert button components and answer label components   
     self.convert_frame = tkinter.Frame(self.mid_frame) 

# label to display answer 
     self.answer = tkinter.StringVar() 
     self.answer_label = tkinter.Label(self.convert_frame, textvariable=self.answer) 
     self.answer_label.pack(side='bottom') 
# convert button for actual conversion 
     self.convert_button = tkinter.Button(self.convert_frame, text='Convert', command=self.do_convert)################################## 
     self.convert_button.pack(side='top') 
##################################################### 
     ##Consider creating either error box or popup 

# create a bottom frame for miscellaneous buttons 
     self.bottom_frame = tkinter.Frame(self.main_window) 
     # instructions button that makes popup box telling how to use app 
     self.instructions_button = tkinter.Button(self.bottom_frame, text='Instructions', command=self.instructions) 
     self.instructions_button.pack(side='left') 
# quit button that quits app 
     self.quit_button = tkinter.Button(self.bottom_frame, text='Quit', command=self.main_window.destroy) 
     self.quit_button.pack(side='right') 
##############################################  
# packup the frames 
     self.from_list_frame.pack(side='left') 
     self.to_list_frame.pack(side='left') 

     self.lists_frame.pack(side='left') 
     self.convert_frame.pack(side='left') 
     self.entry_frame.pack(side='right') 



     self.mid_frame.pack(side ='top') 
     self.bottom_frame.pack(side='bottom') 
     # enter main loop 

     tkinter.mainloop() 
     #print(self.from_radio.get(), self.to_radio.get(), self.temp_entry)#### 
    def instructions(self): 
     tkinter.messagebox.showinfo('Instructions', 'This application allows the user to convert a temperature between Fahrenheit, Celsius, and Kelvin. '\ 
     'A user may select a unit to convert from, a unit to convert to, and what temperature they would like to convert. '\ 
      'Using this information they may convert the entered temperature into the desired unit.') 
######################################### 
# called by the convert button, uses from_radio selection to decide who to convert into(which conversion function to call) 
    def do_convert(self): 
     #self.converted_temp = None 
     if self.from_radio == 'FAHRENHEIT': 
      converted_temp = f_convert() 
     elif self.from_radio == 'CELSIUS': 
      converted_temp = c_convert() 
     elif self.from_radio == 'KELVIN': 
      converted_temp = k_convert() 
# sets self.answer(and so answer label) to value returned into converted_temp 
     self.answer.set(converted_temp) 
########################################################### 
# series of functions for each individual unit to hold conversion formulas for each possible case 
# using self.to_radio selection to decide which conversion to perform, then returns the resulting temperature 
# for use in do_convert 
    def f_convert(self): 
     if self.to_radio == 'FAHRENHEIT': 
      new_temp = self.temp_entry 
     elif self.to_radio == 'CELSIUS': 
      new_temp = (self.temp_entry - 32)*(5/9.0) 
     elif self.to_radio == 'KELVIN': 
      new_temp = (self.temp_entry + 459.67)*(5/9.0) 

     return new_temp 

    def c_convert(self): 
     if self.to_radio == 'FAHRENHEIT': 
      new_temp = (9/5.0)*self.temp_entry + 32.0 
     elif self.to_radio == 'CELSIUS': 
      new_temp = self.temp_entry 
     elif self.to_radio == 'KELVIN': 
      new_temp = self.temp_entry + 273.15 

     return new_temp 

    def k_convert(self): 
     if self.to_radio == 'FAHRENHEIT': 
      new_temp = (9/5.0)*(self.temp_entry-273.15) + 32 
     elif self.to_radio == 'CELSIUS': 
      new_temp = self.temp_entry - 273.15 
     elif self.to_radio == 'KELVIN': 
      new_temp = self.temp_entry 

     return new_temp 

conv_gui = TempConverterGUI() 

Answer 1

的代码可以重新因素 - 有很多重复的 - 但我只提了两件事情，实际上是导致错误：

1. .get()方法self.from_radio永远不会被调用。
2. 调用类方法之前缺少self S，从而为f_convert()，c_convert()等

例子：

def do_convert(self): 
    if self.from_radio == 'FAHRENHEIT': <---- missing ".get()" after "self.from_radio" 
     converted_temp = f_convert() <---- missing "self" before f_convert() 
    elif self.from_radio == 'CELSIUS': 
     converted_temp = c_convert()  
    elif self.from_radio == 'KELVIN':  
     converted_temp = k_convert()  
    self.answer.set(converted_temp) 

你可以将其重新写这样的事：

def do_convert(self): 
    radio_value = self.from_radio.get() 
    if radio_value == 'FAHRENHEIT': 
     converted_temp = self.f_convert() 
    elif radio_value == 'CELSIUS': 
     converted_temp = self.c_convert() 
    elif radio_value == 'KELVIN': 
     converted_temp = self.k_convert() 
    self.answer.set(converted_temp) 

Answer 2

你得到的错误，因为你忘了使用tkinter.StringVar类型的self.from_radio对象的get()方法来检索它的当前值。由于没有任何if语句为真，并且本地变量converted_temp未定义，因为在引用它之前它从未分配过值。

下面是修改后的版本显示的一种方式，以避免该问题：

# called by the convert_button, uses from_radio selection to 
    # decide what to convert into (i.e. which conversion function to call) 
     def do_convert(self): 
      converted_temp = '' # default if somehow there's no match 
      from_radio = self.from_radio.get() 
      if from_radio == 'FAHRENHEIT': 
       converted_temp = f_convert() 
      elif from_radio == 'CELSIUS': 
       converted_temp = c_convert() 
      elif from_radio == 'KELVIN': 
       converted_temp = k_convert() 

      self.answer.set(converted_temp)