title: TypeError: unsupported operand type(s) for +: 'dict_keys' and 'list'
body: <p>I am trying to use a Python package called bidi.
  In a module in this package (algorithm.py) there are some lines that give me error, although it is part of the package.</p>
  
  <p>Here are the lines:</p>
  
  <pre><code>_LEAST_GREATER_ODD = lambda x: (x + 1) | 1
  _LEAST_GREATER_EVEN = lambda x: (x + 2) &amp; ~1
  
  X2_X5_MAPPINGS = {
      'RLE': (_LEAST_GREATER_ODD, 'N'),
      'LRE': (_LEAST_GREATER_EVEN, 'N'),
      'RLO': (_LEAST_GREATER_ODD, 'R'),
      'LRO': (_LEAST_GREATER_EVEN, 'L'),
  }
  
  # Added 'B' so X6 won't execute in that case and X8 will run its course
  X6_IGNORED = X2_X5_MAPPINGS.keys() + ['BN', 'PDF', 'B']
  X9_REMOVED = X2_X5_MAPPINGS.keys() + ['BN', 'PDF']
  </code></pre>
  
  <p>If I run the code in Python 3 I get this error message:</p>
  
  <pre><code>Traceback (most recent call last):
    File "&lt;pyshell#9&gt;", line 1, in &lt;module&gt;
      from bidi.algorithm import get_display
    File "C:\Python33\lib\site-packages\python_bidi-0.3.4-py3.3.egg\bidi\algorithm.py", line 41, in &lt;module&gt;
      X6_IGNORED = X2_X5_MAPPINGS.keys() + ['BN', 'PDF', 'B']
  TypeError: unsupported operand type(s) for +: 'dict_keys' and 'list'
  </code></pre>
  
  <p>Why there is this error although this is part of the bidi package? Does it have anything to do with my Python version? I appreciate any help on this.</p>