Strange threading behaviour
d at davea.name
Thu Jun 21 19:07:02 CEST 2012
On 06/21/2012 11:19 AM, Rotwang wrote:
> Hi all, I'm using Python 2.7.2 on Windows 7 and a module I've written
> is acting strangely. I can reproduce the behaviour in question with
> the following:
> --- begin bugtest.py ---
> import threading, Tkinter, os, pickle
> class savethread(threading.Thread):
> def __init__(self, value):
> self.value = value
> def run(self):
> print 'Saving:',
> with open(os.path.join(os.getcwd(), 'bugfile'), 'wb') as f:
> pickle.dump(self.value, f)
> print 'saved'
> class myclass(object):
> def gui(self):
> root = Tkinter.Tk()
> def save(event):
> root.bind('s', save)
> m = myclass()
> --- end bugtest.py ---
> Here's the problem: suppose I fire up Python and type
> >>> import bugtest
> and then click on the Tk window that spawns and press 's'. Then
> 'Saving:' gets printed, and an empty file named 'bugfile' appears in
> my current working directory. But nothing else happens until I close
> the Tk window; as soon as I do so the file is written to and 'saved'
> gets printed. If I subsequently type
> >>> bugtest.m.gui()
> and then click on the resulting window and press 's', then 'Saving:
> saved' gets printed and the file is written to immediately, exactly as
> I would expect. Similarly if I remove the call to m.gui from the
> module and just call it myself after importing then it all works fine.
> But it seems as if calling the gui within the module itself somehow
> stops savethread(self).run from finishing its job while the gui is
> still alive.
> Can anyone help?
I did not study your code, as I'm not very familiar with tkinter.
However, I think I know your problem:
You do not want to try to start up threads from within a import. An
import is special, and somehow blocks threading while it's running.
Consequently, a module should not try to do anything too fancy from
within its top-level code. Add in the traditional:
m = myclass()
if __name__ == "__main__":
and just run it from the command line, as python bugtest.py
And if you want to run it from a interactive python session, do the call
to main() after importing it:
>>>> import bugtest
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