title: Membership for list of arrays: ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all() error problem
body: <pre><code>Q = [np.array([0, 1]), np.array([1, 2]), np.array([2, 3]), np.array([3, 4])]
  for q in Q:
      print(q in Q)
  </code></pre>
  <p>Running the code above, it gives me the result 'True' at the first iteration, while ValueError comes out afterwards.</p>
  <blockquote>
  <p>True</p>
  </blockquote>
  <blockquote>
  <p>ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()</p>
  </blockquote>
  <p>I have no idea why it starts to go wrong at second iteration. Anybody can help me plz..</p>