title: Change values in list of dictioneries
body: <p>I have huge lists of dictionaries and i must to change date format in key <code>&lt;DATE&gt;</code> in each dictionary on list.</p>
  <p>I write code like that but it doesn't work:</p>
  <pre><code>dict_list = [
      {'&lt;TICKER&gt;': 'HDR', '&lt;DATE&gt;': '19980317', '&lt;CLOSE&gt;': '11.633', '&lt;VOL&gt;': '67931'},
      {'&lt;TICKER&gt;': 'HDR', '&lt;DATE&gt;': '19980318', '&lt;CLOSE&gt;': '10.481', '&lt;VOL&gt;': '115169'},
      {'&lt;TICKER&gt;': 'HDR', '&lt;DATE&gt;': '19980319', '&lt;CLOSE&gt;': '10.131', '&lt;VOL&gt;': '75305'},
      {'&lt;TICKER&gt;': 'HDR', '&lt;DATE&gt;': '19980320', '&lt;CLOSE&gt;': '10.481', '&lt;VOL&gt;': '53504'},
      {'&lt;TICKER&gt;': 'HDR', '&lt;DATE&gt;': '19980323', '&lt;CLOSE&gt;': '10.379', '&lt;VOL&gt;': '27581'},
      {'&lt;TICKER&gt;': 'HDR', '&lt;DATE&gt;': '19980324', '&lt;CLOSE&gt;': '10.228', '&lt;VOL&gt;': '37328'},
      {'&lt;TICKER&gt;': 'HDR', '&lt;DATE&gt;': '19980325', '&lt;CLOSE&gt;': '10.131', '&lt;VOL&gt;': '28739'},
      {'&lt;TICKER&gt;': 'HDR', '&lt;DATE&gt;': '19980326', '&lt;CLOSE&gt;': '10.131', '&lt;VOL&gt;': '45352'},
      {'&lt;TICKER&gt;': 'HDR', '&lt;DATE&gt;': '19980327', '&lt;CLOSE&gt;': '10.027', '&lt;VOL&gt;': '42585'},
      {'&lt;TICKER&gt;': 'HDR', '&lt;DATE&gt;': '19980330', '&lt;CLOSE&gt;': '10.027', '&lt;VOL&gt;': '21260'}
  ]
      
  for dictionary in dict_list:
      for date in dictionary:
          date = dictionary[&quot;&lt;DATE&gt;&quot;]
          year = date[:4]
          month = date[4:6]
          day = date[6:]
          date = f&quot;{year}-{month}-{day}&quot;
  
  print(dict_list)
  </code></pre>
  <p>I try to add:</p>
  <p><code>dictionary.update({&quot;&lt;DATE&gt;&quot;: date})</code></p>
  <p>but output doesn't look good. Should be:</p>
  <p><code>{...'&lt;DATE&gt;': '1998-03-17'...}</code></p>
  <p>was:</p>
  <p><code>{...'&lt;DATE&gt;': '1998------0-3-17'...}</code></p>
  <p>I have no idea how to fix it. Please help.</p>