title: Correct way to update a python dict dynamically
body: <p>I have a python dict containing data about a table.</p>
  
  <pre><code>table_dict = {'0': {'column_metadata': '...',
                      'cells':[[cell1_url],[cell2_url]]
                     },
                '1': {'column_metadata': '...',
                      'cells':[[cell1_url],[cell2_url]]
                     }
               }
  </code></pre>
  
  <p>Here keys are column position ie 0 means first column, 1 is second so on
  each column has a inner dict with a key <strong>cells</strong> which is list of list.</p>
  
  <p>I am iterating over this dict to get cell value from url and then appending it back to same list.</p>
  
  <pre><code>for key, column in table_dict:
      for cell in column['cells']:
          cell_value = get_cell_data(cell1_url)
          column['cells'].append(cell_value)
  </code></pre>
  
  <p>with this code I get final dict as</p>
  
  <pre><code>table_dict = {'0': {'column_metadata': '...',
                      'cells':[[cell1_url, cell1_data],
                               [cell2_url, cell2_data]
                              ]
                     },
                '1': {'column_metadata': '...',
                      'cells':[[cell1_url, cell1_data],
                               [cell2_url, cell2_data]
                              ]
  </code></pre>
  
  <p>I will not delete any keys just add data to dict.</p>
  
  <p>Is this the correct method. Iterating over dict and then append to same.</p>
  
  <p>Is there any better way to approach this problem ?</p>