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Ralsina.Me — Roberto Alsina's website

PyQt Quickie: command line parsing

So, you are writ­ing a PyQt ap­p, and you want it to sup­port com­mand line ar­gu­ments. So you do some­thing like this:

opt_parser = OptionParser()
opt_parser.add_option("-q", dest="quickly", action="store_true",
    help="Do it quickly (default=False)")
(options, args) = opt_parser.parse_args(sys.argv)
app = QApplication(sys.argv)
:
:
:

Or maybe even QAp­pli­ca­tion([]). Ok, you are doing it wrong. And this is wrong in most tutorials, too. Why? Because Qt (and thus PyQt) supports a bunch of useful command line options already. So if you do it like in the first listing, and pass "-style=oxygen" or whatever, one of the following will happen.

  1. Op­t­­Pars­er is go­ing to tell you it's not a valid op­­tion and abort

  2. You will ig­nore the op­­tion and not do any­thing use­­ful with it

  3. You will have your own -style op­­tion and do two things with it

All three out­comes are less than ide­al.

The right way to do this is:

opt_parser = OptionParser()
opt_parser.add_option("-q", dest="quickly", action="store_true",
    help="Do it quickly (default=False)")
app = QApplication(sys.argv)
(options, args) = opt_parser.parse_args(app.arguments())
:
:
:

This way, you give PyQt a chance to process the options it recognizes, and, then, you get to handle the rest, because app.arguments() has all Qt options removed.

The bad side of this is, you will make --help slightly slower, since it will have to build a QApplication to do nothing, and you will have undocumented options. Solution for both problems left as an exercise.

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