code: def source_range_slices(start, end, nr_var_dict):
      
  
      return OrderedDict((k, slice(s,e,1))
          for k, (s, e)
          in source_range_tuple(start, end, nr_var_dict).iteritems())
docs: Given a range of source numbers, as well as a dictionary
      containing the numbers of each source, returns a dictionary
      containing slices for each source variable type.