tkinter listbox insert error "invalid command name ".50054760.50055432" - python-3.x

Question

I have a database of objects and you can view the items in the database in a listbox and there's a button to remove an item and to create an item. Creating an item opens a dialog window for the item class and then the item's data is stored in the database. I have reproduced the problem with a very simple duplicate of my set-up (see code below).
Every time I add a new item, the addition is successful (it's there the next time I open up the database dialog), but the listbox doesn't insert the item, and when I close the database dialog I get the following error:
Exception in Tkinter callback Traceback (most recent call last):
File "C:\Python33\lib\tkinter__init__.py", line 1442, in call
return self.func(*args) File "", line 21, in addRecord File "C:\Python33\lib\tkinter__init__.py", line 2604, in insert
self.tk.call((self._w, 'insert', index) + elements)
_tkinter.TclError: invalid command name ".50054760.50055432"
The same problem doesn't come up if I just try to create the object and populate its values without invoking its inputs GUI (which is necessary for the process of inserting things into my database). I've seen a similar error in another thread (sorry, but I can't seem to find it again), where the problem was with multithreading. I'm not aware of any threading that I'm doing and don't want to download yet another package to handle tkinter threading. Any ideas? Workarounds? I'm using Python v3.3 and 64-bit Windows 7, if that helps.
Here's my simplified database code:
import tkinter
import traceback
# Test =========================================================================
class Test:
def __init__(self):
"""A database of objects' IDs and values."""
self.data = {1: 'a', 2: 'b', 3: 'c'}
#---------------------------------------------------------------------------
def addRecord(self):
"""Opens up a new item for editing and saves that ability to the
database."""
print('hi0')
newItem = OtherObject()
newItem.create(self.root)
print('hi1')
self.data[newItem.ID] = newItem.value
print('hi2')
self.listbox.insert(tkinter.END, self.formatItem(newItem.ID))
print('hi3')
#---------------------------------------------------------------------------
def delRecord(self):
"""Removes selected item from the database."""
try:
index = self.listbox.curselection()[0]
selection = self.listbox.get(index)
except:
return
ID = int(selection.split(':')[0])
self.data.pop(ID)
self.listbox.delete(index)
#---------------------------------------------------------------------------
def dataframe(self, master):
"""Assembles a tkinter frame with a scrollbar to view database objects.
(Returns Frame, Scrollbar widget, Listbox widget)
master: (Tk or Toplevel) tkinter master widget."""
frame = tkinter.Frame(master)
# scrollbar
scrollbar = tkinter.Scrollbar(frame)
scrollbar.pack(side=tkinter.LEFT, fill=tkinter.Y)
# listbox
listbox = tkinter.Listbox(frame, yscrollcommand=scrollbar.set)
listbox.pack(side=tkinter.LEFT, fill=tkinter.BOTH)
# fill listbox
for ID in self.data:
listbox.insert(tkinter.END, self.formatItem(ID))
return (frame, listbox, scrollbar)
#---------------------------------------------------------------------------
def destroyLB(self, e):
for line in traceback.format_stack():
print(line.strip())
#---------------------------------------------------------------------------
def formatItem(self, ID):
"""Creates a nice string representation of an item in the database."""
return '{0}:{1}'.format(ID, self.data[ID])
#---------------------------------------------------------------------------
def listboxSelect(self, e):
"""Manages events when the selection changes in the database interface.
e: (Event) tkinter event."""
try:
selection = self.listbox.get(self.listbox.curselection()[0])
except:
return
# set description label
ID = int(selection.split(':')[0])
self.lblstr.set(self.data[ID])
#---------------------------------------------------------------------------
def view(self):
"""Displays database interface."""
self.root = tkinter.Tk()
# listbox frame
self.frame, self.listbox, self.scrollbar = self.dataframe(self.root)
self.frame.grid(column=0, row=0)
self.listbox.bind('<<ListboxSelect>>', self.listboxSelect)
self.listbox.bind('<Destroy>', self.destroyLB)
# record display frame
self.lblstr = tkinter.StringVar()
self.lbl = tkinter.Label(self.root, textvariable=self.lblstr)
self.lbl.grid(column=1, row=0, sticky=tkinter.N)
# buttons frame
self.frame_btn = tkinter.Frame(self.root)
self.frame_btn.grid(row=1, columnspan=2, sticky=tkinter.E+tkinter.W)
# 'create new' button
self.btn_new = tkinter.Button(
self.frame_btn, text='+', command=self.addRecord)
self.btn_new.grid(row=0, column=0)
# 'delete record' button
self.btn_del = tkinter.Button(
self.frame_btn, text='-', command=self.delRecord)
self.btn_del.grid(row=0, column=1)
# display
self.root.mainloop()
# Test =========================================================================
# OtherObject ==================================================================
class OtherObject:
"""An object with an ID and value."""
def __init__ (self):
self.ID = 0
self.value = ''
#---------------------------------------------------------------------------
def create(self, master=None):
"""open a dialog for the user to entry a new object ID and value.
master: (Tk or Toplevel) tkinter master widget."""
self.stuff = tkinter.Toplevel(master)
# ID
tkinter.Label(self.stuff, text='ID: ').grid(row=0, column=0)
self.IDvar = tkinter.StringVar(self.stuff)
self.IDvar.set(self.ID)
IDwidget = tkinter.Entry(self.stuff, textvariable=self.IDvar)
IDwidget.grid(row=0, column=1)
# value
tkinter.Label(self.stuff, text='Value: ').grid(row=1, column=0)
self.valueVar = tkinter.StringVar(self.stuff)
self.valueVar.set(self.value)
valueWidget = tkinter.Entry(self.stuff, textvariable=self.valueVar)
valueWidget.grid(row=1, column=1)
# OK button
tkinter.Button(self.stuff, text='OK', command=self.OK).grid(row=2)
self.stuff.mainloop()
#---------------------------------------------------------------------------
def OK(self):
try: self.ID = int(self.IDvar.get())
except: self.ID = 0
self.value = self.valueVar.get()
self.stuff.destroy()
# OtherObject ==================================================================
Thanks in advance

Answer 1

You are creating more than one instance of Tk. Tkinter is not designed to work like that and you will get unexpected behavior. You need to refactor your code so that you create an instance of Tk only once. If you need multiple windows, create instances of Toplevel.
... time passes ... the code in the question gets updated ...
In the updated version of your question you now are creating one instance of Tk, and then instances of Toplevel. This is good. However, you are also calling mainloop more than once which is a problem. Worse, you're redefining self.root which no doubt is part of the problem. You must call mainloop exactly once over the entirety of your program.

Answer 2

Bryan Oakley guided me to the exact problem that I was encountering:
(1) I created a second Tk object in my OtherObject class.
(2) I called mainloop in my OtherObject class.
Only one Tk object should exist and mainloop should only ever be called once, no matter how many windows are to be displayed.