title: ValueError: too many values to unpack error
body: <p>I have this list of lists of pairs of part of speech consist of words and its tags, and I used the following function to iterate over this list and select the pairs that meet if statement but I have an error. This is the list:</p>
  
  <pre><code>[[('After', 'IN'), ('generating', 'VBG')],
   [('generating', 'VBG'), ('all', 'DT')],
   [('all', 'DT'), ('feature', 'NN')],
   [('feature', 'NN'), ('spaces', 'NNS')]]
  </code></pre>
  
  <p>This is the function:</p>
  
  <pre><code>def select_posesPairs(tweet):
      D=[]
      s = getTokenss(tweet)
      for first,second in s:
          for word,tag in second:
              if tag =='NN':
                  D.append(word)
  
      return D
  </code></pre>
  
  <p>And this is the error:</p>
  
  <pre><code>ValueError: too many values to unpack
  </code></pre>