奇怪的行为：使用tkfiledialog的python应用程序，对话框没有第二次打开

Question

I have a python application controlling a testbed for some technical device. Python itself doesn't use a GUI, everything is displayed in a browser and we use socket connections to communicate.

There is one point, where the operator has to save a protocol file and we need a dialog to select this file. I decided to use the Tkinter plugin for that purpose.

So now I have a small module dialogs.py for all the GUI stuff, which is probably quite overdone, but nvm. Here it is:

from Tkinter import Toplevel, Tk
from tkFileDialog import asksaveasfilename, askopenfilename, askdirectory

class Getter:

    def _create(self):
        self.gui = Tk() # create instance
        self.gui.wm_attributes('-topmost', 1) # ensure it is on top
        self.gui.geometry('0x0+0+0') # minimize

    def _destroy(self):
        self.gui.destroy() # destroy instance

    def get(self):
        pass


class SaveFileGetter(Getter):

    def get(self, ext=None, dir=None, file=None):
        self._create()
        filename = asksaveasfilename(parent=self.gui, defaultextension=ext, initialdir=dir, initialfile=file) # show the dialog
        self._destroy()
        return filename

And then there is somewhere in another module:

from helpers.dialogs import SaveFileGetter

# lots of code

def saveOnRemote(self):
    # code
    protocolFilePath = SaveFileGetter().get(ext='.html')
    # more code

# even more code

When the application runs for the first time everything is fine. But when run the 2nd time, the program reaches the line

self.gui = Tk()

and nothing happens. No dialog does open, there is no exception, no beeping, nothing. The program is so to speak frozen. The CPU usage stays high, so obviously there is something happening in the background, but the application itself doesn't move forward.

To make things weird: If I use Toplevel() instead of Tk() the dialog does open multiple times, but occasionally there is an exception at the same line of code:

self.gui = Toplevel()

The error displayed is:

File "C:/path/to/my/project/somepythonfile.py", line 324, in saveOnRemote
protocolFilePath = SaveFileGetter().get(ext='.html')
File "C:/path/to/my/project/dialogs.py", line 22, in get
self._create()
File "C:/path/to/my/project/dialogs.py", line 8, in _create
self.gui = Toplevel()
File "C:\Python27\lib\lib-tk\Tkinter.py", line 2129, in __init__
BaseWidget.__init__(self, master, 'toplevel', cnf, {}, extra)
File "C:\Python27\lib\lib-tk\Tkinter.py", line 2086, in __init__
(widgetName, self._w) + extra + self._options(cnf))
TclError: out of stack space (infinite loop?)

And for master weirdness, this may happen at any time it seems, at the third execution, at the tenth ... or later. Later in operation it will be used maybe once per hour, but I can't accept that as the operator would have to restart the program to make it work properly again and btw cannot save the protocol file at that moment.

I already wrote a little standalone script, requesting the save file dialog in an endless loop. Everything works as wanted using Tk() or Toplevel(), even without the self.gui.destroy() part.

So there must be something else in my application causing this behaviour. Of course I cannot show the whole code (too much, company work etc.) and I imagine it's hard to guess for you. None of my colleagues has a clue, I myself just started the 3rd month of being a software developer and am clueless as well.

So if you have the tiniest approach of an idea, what could be the reason, please tell me.

---

Inspired by rolika's comment I changed my Getter class to:

class Getter:

    def __init__(self):
        self.gui = Tk()
        self.gui.wm_attributes('-topmost', 1)
        self.gui.geometry('0x0+0+0')

    def __del__(self):
        self.gui.destroy()

Unfortunately it doesn't change anything visibly.

Answer 1

This really is just a suggestion:

Have you tried it without supplying a parent? Parent is optional, and if you don't supply, the dialog pops up over your app's root window.

Please see it here: http://infohost.nmt.edu/tcc/help/pubs/tkinter/web/tkFileDialog.html

Answer 2

Just for the records, although it is no real answer, but a solution. I'm using wxPython instead of Tkinter now. So this is my Getter class:

import wx

class Getter():

    def __init__(self):

        self.app = wx.App()
        self.frame = wx.Frame(None, -1, style=wx.CAPTION, size=(0, 0))

    def __del__(self):

        self.app.Destroy()

    def saveFile(self, ext='*.*', dir='', file='', title=''):

        dialog = wx.FileDialog(self.frame, title, dir, file, '|'+ext, wx.FD_SAVE | wx.FD_OVERWRITE_PROMPT)
        dialog.ShowModal()
        return dialog.GetPath()

And it works, every time.