我的代码中出现KeyError:''，我不知道为什么

Question

它运行良好，但当我关闭窗口时，出现一个keyError:“”。它从所选的键中获取值，但我不明白为什么要给我这些。我希望能在这里得到一些帮助。 我澄清了字典是string:string，我将连接以获得一个string变量，然后执行一些操作。我加上combo1和combo2是固定的字符串。问题是它在var2中连接并工作，但之后会出现此错误

from tkinter import *
from tkinter import ttk
import sqlite3    

class dd:
   def __init__(self, window):
       self.wind = window

       def setvalue(event):
             var = str(self.combo1.get()) + "-" + str(self.combo2.get()) + "-"
             var2 = self.get_eln()[self.combo3.get()] + "-" + self.get_esr([self.combo4.get()]
             self.var3 = var + var2

       frame = LabelFrame(self.wind, text='Data', height = 50, width = 1000, bd=4)
       frame.grid(row=0, column=0, sticky=W+E)
       frame.grid_propagate(0)


       #Combo box 3
       self.combo3 = ttk.Combobox(frame, value=list(self.get_eln().keys()), width=60)
       self.combo3.bind("<<ComboboxSelected>>", setvalue)
       self.combo3.grid(row=1, column=4, pady=4, sticky=W)

       #Combo box 4
       self.combo4 = ttk.Combobox(frame, value=list(self.get_esr().keys()),width=20)
       self.combo4.bind("<<ComboboxSelected>>", setvalue)
       self.combo4.grid(row=1, column=6, pady=4, sticky=W)

   def run_query(self, query, parameters = ()):
       with sqlite3.connect(self.db) as conn:
           cursor = conn.cursor()
           result = cursor.execute(query, parameters)
           conn.commit()
       return result

   def get_eln(self):
       query = 'SELECT Eln, E_a FROM Elns'
       db_rows = self.run_query(query)
       return {Eln:E_a for Eln, E_a in db_rows}

   def get_esr(self):
       query = 'SELECT Esr, Est_a FROM Ess'
       db_rows = self.run_query(query)
       return {Esr:Est_a for Esr,Est_a in db_rows}


if __name__ == '__main__':
   window = Tk()
   application = a(window)
   window.mainloop()

当我关闭窗口时，将显示以下内容：

Exception in Tkinter callback
Traceback (most recent call last):
  File "Python\Python38-32\lib\tkinter\__init__.py", line 1883, in __call__
    return self.func(*args)
  File "code.py", line 6, in setvalue
    var2 = self.get_eln()[self.combo3.get()] + "_" + self.get_esr()[self.combo4.get()]
KeyError: ''
Exception in Tkinter callback
Traceback (most recent call last):
  File "C:Python\Python38-32\lib\tkinter\__init__.py", line 1883, in __call__
    return self.func(*args)
  File "code.py", line 6, in setvalue
    var2 = self.get_eln()[self.combo3.get()] + "_" + self.get_esr()[self.combo4.get()]
KeyError: ''

我认为错误在于VAR2的串联

Answer 1

正如我在评论中所说，问题似乎是试图从self.get_eln()和self.get_esr()返回的dict中获取值，而self.combo3或self.combo4没有值

我想您可以在尝试这样做之前检查两者是否都有值：

if self.combo3.get() and self.combo4.get():
    var2 = self.get_eln()[self.combo3.get()] + "-" + self.get_esr([self.combo4.get()]
else:
    var2 = '' # not sure which value you want for this var

这样你就可以确保你不会得到KeyError

否则，如果您希望对try ... except采用另一种方法，您可以执行以下操作

try:
    var2 = self.get_eln()[self.combo3.get()] + "-" + self.get_esr([self.combo4.get()]
except KeyError:
    # make sure you don't want to 
    var2 = ''

我不想给你一个简单的复制粘贴的答案，所以如果你不明白的东西，只是评论，我会尽力帮助你