title: How to partition list so that there are no partitions with same characters
body: <p>So first  I want to partition list to every possible partition, without changing the order of list.
  Like this:</p>
  <pre><code>[['a', 'b', 'a']]
  [['a'], ['b', 'a']]
  [['a', 'b'], ['a']]
  [['a'], ['b'], ['a']]
  </code></pre>
  <p>Count of ways to do this is 4. I want to remove all possible partitions that have same characters in the part.
  For same input than last time:</p>
  <pre><code>[['a'], ['b', 'a']]
  [['a', 'b'], ['a']]
  [['a'], ['b'], ['a']]
  </code></pre>
  <p>Removed     [['a', 'b', 'a']]    , because it has 2 a's in same part.
  How to do it in python?</p>