title: Selecting pandas cells with None value
body: <p>I have a column of a pandas dataframe that I got from a database query with blank cells. The blank cells become "None" and I want to check if each of the rows is None:         </p>
  
  <pre><code>In [325]: yes_records_sample['name']
  Out[325]: 
  41055    John J Murphy Professional Building
  25260                                   None
  41757             Armand Bayou Nature Center
  31397                                   None
  33104               Hubert Humphrey Building
  16891                         Williams Hall
  29618                                   None
  3770                          Covenant House
  39618                                   None
  1342       Bhathal Student Services Building
  20506                                   None
  </code></pre>
  
  <p>My understanding per the documentation is that I can check if each row is null with <code>isnull()</code> command <a href="http://pandas.pydata.org/pandas-docs/dev/missing_data.html#values-considered-missing" rel="nofollow noreferrer">http://pandas.pydata.org/pandas-docs/dev/missing_data.html#values-considered-missing</a></p>
  
  <p>That function, however, is not working for me:  </p>
  
  <pre><code>In [332]: isnull(yes_records_sample['name'])
  </code></pre>
  
  <p>I get the following error:</p>
  
  <pre><code>NameError Traceback (most recent call last)
  &lt;ipython-input-332-55873906e7e6&gt; in &lt;module&gt;()
  ----&gt; 1 isnull(yes_records_sample['name'])
  NameError: name 'isnull' is not defined
  </code></pre>
  
  <p>I also saw that someone just replaced the "None" strings, but neither of these variations on that approach worked for me:
  <a href="https://stackoverflow.com/questions/24619145/rename-none-value-in-pandas">Rename &quot;None&quot; value in Pandas</a></p>
  
  <pre><code>yes_records_sample['name'].replace('None', "--no value--")
  yes_records_sample['name'].replace(None, "--no value--")
  </code></pre>
  
  <p>I was ultimately able to use the <code>fillna</code> function and fill each of those rows with an empty string <code>yes_records_sample.fillna('')</code> as a workaround and then I could check <code>yes_records_sample['name']==''</code> But I am profoundly confused by how 'None' works and what it means.  Is there a way to easily just check if a cell in a dataframe is 'None'? </p>