title: Argparse - configparser.Interpolation missing option error
body: <p>I am using Argparse for fetching the necessary value from config file.</p>
  
  <p>For example:</p>
  
  <pre><code>python arg.py --event_conf=/opt/open-stack-tools/track_events.conf --openstack_conf=/etc/nova/nova.conf
  </code></pre>
  
  <p>I need to fetch value from two different files.</p>
  
  <p>I can be able to get the results as needed for one local config file.</p>
  
  <p>But In case of fetching the necessary values from nova.conf file, it results in following error: </p>
  
  <pre><code>       Traceback (most recent call last):
            File "arg.py", line 36, in &lt;module&gt;
              oslo_messaging_rabbit= dict(config.items("oslo_messaging_rabbit"))
            File "/usr/lib/python2.7/ConfigParser.py", line 655, in items
              for option in options]
            File "/usr/lib/python2.7/ConfigParser.py", line 691, in _interpolate
              self._interpolate_some(option, L, rawval, section, vars, 1)
            File "/usr/lib/python2.7/ConfigParser.py", line 723, in _interpolate_some
              option, section, rest, var)
  ConfigParser.InterpolationMissingOptionError: Bad value substitution:
          section: [oslo_messaging_rabbit]
          option : logging_exception_prefix
          key    : color
          rawval : %(asctime)s.%(msecs)03d TRACE %(name)s %(instance)s
  </code></pre>
  
  <p>Is there any way to fix the same.</p>
  
  <p>I have copied the necessary contents and created a new local file, I can see that it is working fine.</p>
  
  <p>When I am using the nova.conf file it results in error.</p>
  
  <p>I can't change the file which I am using.</p>
  
  <p>So I need a fix for the particular error.</p>
  
  <p><strong>Note:</strong></p>
  
  <p>Adding more details as needed:</p>
  
  <pre><code>parser.add_argument("-c", "--event_conf",
                      help="Specify config file 1", metavar="FILE")
  args1, remaining_argv1 = parser.parse_known_args()
  
  
  parser.add_argument("-o", "--openstack_conf",
                      help="Specify config file 2", metavar="FILE")
  args2, remaining_argv2 = parser.parse_known_args()
  
  
  if args1.event_conf:
      config = ConfigParser.SafeConfigParser()
      print config.read([args1.event_conf])
      config.read([args1.event_conf])
      configdetails_section1 = dict(config.items("configdetails_section1"))
  </code></pre>