title: JSON serialization of MongoDB ObjectID (ex-scope query)
body: <p>I am confused howcome the variable temp_dict is available outside else condition? when I am saving the array to MongoDB which is setting the ObjectId on each item in the array. Json parser doesn't doesn't know how to serialize ObjectId. </p>
  
  <pre><code>def read_temporary_file(filename, has_header=False):
      wb = load_workbook(filename=filename, use_iterators=True)
      ws = wb.get_active_sheet()  # ws is now an IterableWorksheet
  
      headers = []
      rows = []
      documents = []
  
      for row in ws.iter_rows():  # it brings a new method: iter_rows()
          if has_header:
              has_header = False
              for cell in row:
                  headers.append(cell.internal_value)
          else:
              temp_dict = OrderedDict()
              for cell in row:
                  temp_dict[cell.column] = cell.internal_value
              rows.append(temp_dict)
              documents.append(temp_dict)
  
      print("Saving documents to MongoDB")
      __save(documents)
      print("Printing %s" % temp_dict)
      return (headers, rows)
  </code></pre>