title: Groupby a list of dicts with multiple keys doesn't work even if I use sorted before
body: <p>I have a list of dictionaries like that :</p>
  <pre><code>a = [
      {'user_id':'111','clean_label':'VIR SEPA'},
      {'user_id':'112','clean_label':'VIR SEPA'},
      {'user_id':'111','clean_label':'VIR SEPA'},
  ]
  </code></pre>
  <p>and I want that :</p>
  <pre><code>a = [
      [
          {'user_id':'111','clean_label':'VIR SEPA'},
          {'user_id':'111','clean_label':'VIR SEPA'}
      ],
      [
          {'user_id':'112','clean_label':'VIR SEPA'}
      ]
  ]
  </code></pre>
  <p>I tried with sorted and groupby from itertools like that :</p>
  <pre><code>sorted(a,key=lambda x: (x['user_id'],x['clean_label']))
  [ [tr for tr in tr_per_user_id_clean_label] for key, tr_per_user_id_clean_label in itertools.groupby(a, key=lambda x: (x['user_id'], x['clean_label'])) ]
  </code></pre>
  <p>but I get that :</p>
  <pre><code>[[{'user_id': '111', 'clean_label': 'VIR SEPA'}],
   [{'user_id': '112', 'clean_label': 'VIR SEPA'}],
   [{'user_id': '111', 'clean_label': 'VIR SEPA'}]]
  </code></pre>
  <p>Can someone help me ??</p>
  <p>*Edit : when I sort a :</p>
  <pre><code>[{'user_id': '111', 'clean_label': 'VIR SEPA'},
   {'user_id': '111', 'clean_label': 'VIR SEPA'},
   {'user_id': '112', 'clean_label': 'VIR SEPA'}]
  </code></pre>