title: python pandas: filter out records with null or empty string for a given field
body: <p>I am trying to filter out records whose field_A is null or empty string in the data frame like below:</p>
  
  <pre><code>my_df[my_df.editions is not None]
  my_df.shape
  </code></pre>
  
  <p>This gives me error:</p>
  
  <pre><code>---------------------------------------------------------------------------
  KeyError                                  Traceback (most recent call last)
  &lt;ipython-input-40-e1969e0af259&gt; in &lt;module&gt;()
        1 my_df['editions'] = my['editions'].astype(str)
  ----&gt; 2 my_df = my_df[my_df.editions is not None]
        3 my_df.shape
  
  /home/edamame/anaconda2/lib/python2.7/site-packages/pandas/core/frame.pyc in __getitem__(self, key)
     1995             return self._getitem_multilevel(key)
     1996         else:
  -&gt; 1997             return self._getitem_column(key)
     1998 
     1999     def _getitem_column(self, key):
  
  /home/edamame/anaconda2/lib/python2.7/site-packages/pandas/core/frame.pyc in _getitem_column(self, key)
     2002         # get column
     2003         if self.columns.is_unique:
  -&gt; 2004             return self._get_item_cache(key)
     2005 
     2006         # duplicate columns &amp; possible reduce dimensionality
  
  /home/edamame/anaconda2/lib/python2.7/site-packages/pandas/core/generic.pyc in _get_item_cache(self, item)
     1348         res = cache.get(item)
     1349         if res is None:
  -&gt; 1350             values = self._data.get(item)
     1351             res = self._box_item_values(item, values)
     1352             cache[item] = res
  
  /home/edamame/anaconda2/lib/python2.7/site-packages/pandas/core/internals.pyc in get(self, item, fastpath)
     3288 
     3289             if not isnull(item):
  -&gt; 3290                 loc = self.items.get_loc(item)
     3291             else:
     3292                 indexer = np.arange(len(self.items))[isnull(self.items)]
  
  /home/edamame/anaconda2/lib/python2.7/site-packages/pandas/indexes/base.pyc in get_loc(self, key, method, tolerance)
     1945                 return self._engine.get_loc(key)
     1946             except KeyError:
  -&gt; 1947                 return self._engine.get_loc(self._maybe_cast_indexer(key))
     1948 
     1949         indexer = self.get_indexer([key], method=method, tolerance=tolerance)
  
  pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4154)()
  
  pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:4018)()
  
  pandas/hashtable.pyx in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:12368)()
  
  pandas/hashtable.pyx in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:12322)()
  
  KeyError: True
  </code></pre>
  
  <p>or</p>
  
  <pre><code>my_df[my_df.editions != None]
  my_df.shape
  </code></pre>
  
  <p>This one gave no error but didn't filter out any None values. </p>
  
  <p>I also tried:</p>
  
  <pre><code>my_df = my_df[my_df.editions.notnull()]
  </code></pre>
  
  <p>This one doesn't give error but doesn't filter out any None values either.</p>
  
  <p>Could anyone please advise how to solve this problem? Thanks!</p>