tkinter need to click in shell to get gui fields to update - python-3.x

Question

I have a tkinter gui with Python 3.4.2 in which there are various buttons, a user entry field and a text field. Everything works except that I appear to have to click in the Python shell (IDLE) and out of the gui to get fields to update in response to button presses. The updates are immediate when I click on the shell. I have copied this tkintergui from http://ubuntuforums.org/showthread.php?t=1156637 which gives the same problem on my Mac. Immediate update if IDLE shell clicked or very slow update in the GUI
#!/usr/bin/python
from tkinter import *
from tkinter.filedialog import *
class SimpleEdApp:
def __init__(self, parent=Tk()):
self.mainWindow = (parent)
self.mainWindow.title("Simple Editor")
self.mainWindow.resizable(0, 0)
self.make_mnu()
self.make_txt()
def make_txt(self):
self.text = Text(self.mainWindow, width = 80, height = 40, background = 'white')
self.scrollY = Scrollbar(self.mainWindow, orient = VERTICAL, command = self.text.yview, troughcolor = 'white')
self.text["yscrollcommand"] = self.scrollY.set
self.scrollY.pack(side = RIGHT, fill = Y)
self.text.pack(expand = TRUE, fill = BOTH)
def make_mnu(self):
self.menubar = Menu(self.mainWindow)
self.filemenu = Menu(self.menubar, tearoff = 0)
self.filemenu.add_command(label = "Open", command = self.file_open)
self.filemenu.add_command(label = "Save as...", command = self.file_save)
self.filemenu.add_separator()
self.filemenu.add_command(label = "Exit", command = self.mainWindow.destroy)
self.menubar.add_cascade(label = "File", menu = self.filemenu)
self.mainWindow.config(menu = self.menubar)
def file_open(self):
filename =askopenfilename(filetypes=[("pythonfiles","*.py"),("tclfiles","*.tcl"),("allfiles","*")])
f = open(filename, 'r')
data = f.read()
f.close()
self.text.delete(1.0, END)
self.text.insert(1.0, data)
def file_save(self):
filename =asksaveasfilename(filetypes=[("pythonfiles","*.py"),("tclfiles","*.tcl"),("allfiles","*")])
f = open(filename, 'w')
data = self.text.get(1.0, END)
f.write(data)
f.close()
app = SimpleEdApp()
app.mainWindow.mainloop()
Grateful for correct implementation

Answer 1

There is nothing wrong with your code. This looks to be a bug in IDLE.
In the comments you asked how to run the program outside of IDLE. To do that, open up a prompt and type the command python myfile.py, where myfile.py is the name of your python file (assuming "python" is in your PATH).
*note: depending on what is installed in your system, you may need to use python3 rather than python.