Re: [Qemu-devel] [PATCH for-2.11 v2 1/5] qmp-shell: Use optparse module

["Daniel P. Berrange" <berrange@redhat.com>]

On Tue, Aug 15, 2017 at 11:47:28AM +0200, Markus Armbruster wrote:
> Eduardo Habkost <ehabkost@redhat.com> writes:
> 
> > It makes command-line parsing and generation of help text much
> > simpler.
> 
> There's really no excuse for parsing command line arguments by hand in
> Python.
> 
> > The optparse module is deprecated since Python 2.7, but argparse
> > is not available in Python 2.6 (the minimum Python version
> > required for building QEMU).
> 
> We have a few uses of argparse in the tree.  Are they okay?
> 
> We also use getopt in places.  Perhaps we should pick one way to parse
> command lines and stick to it.

I just came up against this problem with keycodemapdb which I'm adding as
a submodule to qemu.  I used argparse there because it is the modern
recommended API for python >= 2.7.   I examined possibilty of using
optparse instead, but it lacks key features - in particular the idea
of 'subcommands' is entirely missing from optparse.

The 'argparse' module is part of python core, but is *also* available
as a standalone module that is implemented in terms of optparse.

So, I would suggest that we just copy the 'argparse' module into the
QEMU 'scripts/thirdparty' directory.

Then in any files which need argparse, you can do this

  try:
      import argparse
  except:
      import os, sys
      sys.path.append(os.path.join(os.path.dirname(__file__), "thirdparty"))
      import argparse

so that it tries to use the argparse provided by python, and falls back
to pulling in the one in our scripts/thirdparty directory.

When we finally bump our min python to 2.7, we can simply drop this
compat code for the import statement.  This avoids need for us to
re-write code to use a deprecated API, with a worse feature set.

Regards,
Daniel
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