title: How to get product without repeating elements
body: <p>For example, for code like this</p>
  <pre><code>from itertools import product
  lst = [[1,2], [2,3], [4,5,6]]
  for i in product(*lst):
      print(i)
  </code></pre>
  <p>I get</p>
  <pre><code>(1, 2, 4)
  (1, 2, 5)
  (1, 2, 6)
  (1, 3, 4)
  (1, 3, 5)
  (1, 3, 6)
  (2, 2, 4)
  (2, 2, 5)
  (2, 2, 6)
  (2, 3, 4)
  (2, 3, 5)
  (2, 3, 6)
  </code></pre>
  <p>but I would like to get</p>
  <pre><code>(1, 2, 4)
  (1, 2, 5)
  (1, 2, 6)
  (1, 3, 4)
  (1, 3, 5)
  (1, 3, 6)  
  (2, 3, 4)
  (2, 3, 5)
  (2, 3, 6)
  </code></pre>
  <p>Tell me how this can be done using itertools.</p>