Question

If I’m trying to create a window or prompt a file dialog in the IDLE shell, nothing opens and the shell restarts. Is this a bug of some kind? I can’t find anything about it. I’m new to PyQt (and Python in general) but had been able to get tutorials to work correctly. The last day or so, if I open IDLE and import PyQt4, QtGui, etc and then run something simple like QFileDialog.getOpenFileName, the shell just restarts. Any ideas?

Answer 1

You need to have a QApplication before you can use anything else from PyQt. Try rereading some of the tutorials you followed, or do a few more. This one for example.

In the first code sample of the above tutorial, pay special attention to these lines (I’ve included the comments from the tutorial for convenience):

app = QtGui.QApplication(sys.argv)

Every PyQt4 application must create an application object. The
application object is located in the QtGui module. The sys.argv
parameter is a list of arguments from the command line. Python scripts
can be run from the shell. It is a way, how we can control the startup
of our scripts.

and

sys.exit(app.exec_())

Finally, we enter the mainloop of the application. The event handling
starts from this point. The mainloop receives events from the window
system and dispatches them to the application widgets. The mainloop
ends, if we call the exit() method or the main widget is destroyed.
The sys.exit() method ensures a clean exit. The environment will be
informed, how the application ended.

The exec_() method has an underscore. It is because the exec is a
Python keyword. And thus, exec_() was used instead.

It appears you might have forgotten about these. Or maybe you haven’t realized that this means that you normally can’t use PyQt with a running event loop in the interactive shell. However, there is a trick for that, see here.