title: python argparse: 'Namespace' error
body: <p>I'm trying to build a process with some parsing option, some mandatory and others optinal.
  I have a problem with the following code:</p>
  
  <pre><code>    bandlist=[1,2,3,4,5,6,7,8]
      process=['rad', 'ref', 'radref']
      sensors=['LC', 'LO', 'LE', 'LT']
      series=['4', '5', '7', '8']
      usage = "usage: %prog [options] "
      parser = argparse.ArgumentParser(usage=usage)
  
      parser.add_argument('-d', '--directory', dest='directory', action='store', type=str, \
                        help='complete path of landsat product folder: mydir/filename/')
  
      parser.add_argument('-p', '--process', dest='operation', action='store', choices = process, \
                        help='process requested: radiance, reflectance, both', default='rad')
  
      parser.add_argument('-l', '--series', dest='satellite', action='store', choices = series , \
                        help='Landsat series:4, 5, 7, 8')
  
      parser.add_argument('-s', '--sensor', dest='sensor', action='store', choices = sensors, \
                        help='sensor acronymous, for example LO for Landsat OLI, or LE for Landsat ETM+, etc..', default=None)
  
      parser.add_argument('-o', '--output',   dest='output', type=str, \
              help='Directory of output raster. \n \
                  Unless specified, output directory will be workDirectory/results/datafolder/. \n \
                  If specified, the output directory wil be mydirectory/results/filename/rad (and/or ref)/', default=None)
  
      parser.add_argument('-x', action='store_true', dest='bool', help='activate iterative radiance and/or reflectance computation for all the bands', default=False)
  
      parser.add_argument('-b', '--bands', dest='bands', choices = bandlist, type=int, \
                        help='bands to process', nargs='*', default=None)
  
      (options, args) = parser.parse_args()
  </code></pre>
  
  <p>and there is the following error:</p>
  
  <pre><code>Traceback (most recent call last):
  File "C:\Users\lbernardi\Desktop\extract\LandsatTMroutine_RadiometricCorrection_1.0.py", line 1210, in &lt;module&gt;
  main()
  File "C:\Users\lbernardi\Desktop\extract\LandsatTMroutine_RadiometricCorrection_1.0.py", line 784, in main
  (options, args) = parser.parse_args()
  TypeError: 'Namespace' object is not iterable
  </code></pre>
  
  <p>I don't understand what the error is about.
  Thank for your help</p>