title: Pandas apply lambda to the entire dataframe
body: <p>Can anybody explain me why this code should not work?</p>
  
  <pre><code>wordsCount = {}
  
  def addWord(x):
      print(x)
  
  df.apply(addWord(x))
  </code></pre>
  
  <p>It return the error: TypeError: ("'NoneType' object is not callable", 'occurred at index 0') 
  The dataframe df contains some None value in some cell. My intention is to apply a function to all non-None value.</p>