Fix set_default() with boolean CLI options

Porting to argparse broke set_default() with boolean CLI options. The
new test case shows this borkage.

The issue is that, by default, argparse differs subtly from optparse in
its handling of defaults for boolean options. Compare:

  >>> p = optparse.OptionParser()
  >>> p.add_option('--foo', action='store_true')
  >>> p.add_option('--bar', action='store_true', default=False)
  >>> p.parse_args([])
  (<Values at 0x7f28aba066c8: {'foo': None, 'bar': False}>, [])

to:

  >>> p = argparse.ArgumentParser()
  >>> p.add_argument('--foo', action='store_true')
  >>> p.add_argument('--bar', action='store_true', default=False)
  >>> p.add_argument('--blaa', action='store_true', default=None)
  >>> p.parse_args([])
  Namespace(bar=False, blaa=None, foo=False)

i.e. unless you specify a default for a boolean option, optparse
defaults to None whereas argparse defaults to False. To get the
same optparse behaviour with argparse, you need default=None.

Change-Id: Ifc92a834c4ba59e939d80ac5de24d7051232f5b5

1 files changed, 2 insertions, 1 deletions

diff --git a/openstack/common/cfg.py b/openstack/common/cfg.py
index 28baa04..9be96cc 100644
--- a/openstack/common/cfg.py
+++ b/openstack/common/cfg.py
@@ -632,7 +632,8 @@ class Opt(object):
             kwargs['dest'] = dest
         else:
             kwargs['nargs'] = '?'
-        kwargs.update({'metavar': self.metavar,
+        kwargs.update({'default': None,
+                       'metavar': self.metavar,
                        'help': self.help, })
         return kwargs