title: Replacing empty value with "None" in a python dictionary
body: <p>I have a <strong>Python</strong> dictionary that I generated from an arcgis shapefile.  The dictionary has key = FID (point ID) : value = either nothing or "HH".  The dictionary looks like this:</p>
  
  <pre><code>Cluster_dict = {0: [u' '], 1: [u'HH'], 2: [u'HH'], 3: [u' '], 4: [u' '], 5: [u' '], 6: [u' '], 7: [u' '], 8: [u' '], 9: [u' '], 10: [u' '], 11: [u'HH'], 12: [u'HH'], 13: [u'HH'], 14: [u'HH'], 15: [u' '], 16: [u' '], 17: [u' '], 18: [u' '], 19: [u' '], 20: [u' '], 21: [u' '], 22: [u' '], 23: [u'HH'], 24: [u'HH'], 25: [u' '], 26: [u' '], 27: [u' '], 28: [u' ']....}
  </code></pre>
  
  <p>The extra characters of the value [u' '] and [u'HH'] show up after I created the dictionary from the arcgis shapefile with the following code: </p>
  
  <pre><code>arcpy.ClustersOutliers_stats('input_file', "GRID_CODE", 'output_file',  "INVERSE_DISTANCE", "EUCLIDEAN_DISTANCE", "NONE", "", "")
  Cluster_dict = {}
  sc = arcpy.SearchCursor('output_file')
  for row in sc:
      Cluster_dict[row.FID] = [row.COType]
  
  print Cluster_dict
  </code></pre>
  
  <p>I'm trying to use this dictionary to append to a nested list of each point's 8 (or less) neighbors using the following code:</p>
  
  <pre><code>clusterList = []
  for clist in Neighbors_List:
      row = []
      for ccode in clist:
          row.append(Cluster_dict[ccode])
      clusterList.append(row)
   print clusterList
  </code></pre>
  
  <p>But when it gets to row.append(Cluster_dict[ccode]), I get a <strong>key error '0'</strong>.  I'm thinking this is because there is no value for key 0, but I'm not sure about this.  When I used the following code to replace all the [u' '] with "None", the dictionary doesn't replace the empty values.  I'm using the following code to try and replace [u' '].</p>
  
  <pre><code>for k, v in Cluster_dict.iteritems():
      if v is [u' ']:       #I've also tried '[u' ']'
          Cluster_dict[k] = 'None'
  
  print Cluster_dict 
  </code></pre>
  
  <p>Any help would be appreciated.  Would it be easier to strip [u' '] out of all the values in the dictionary?  If so, can someone show me how to strip unwanted characters out of a dictionary?   </p>
  
  <p>Thanks very much for any help.</p>