title: How to do conditional statements in pandas/python with null values
body: <p>How do I do condition replacements in pandas?</p>
  
  <pre><code>df = pd.DataFrame([[1, 2, 3], [4, None, None], [None, None, 9]])
  </code></pre>
  
  <p>In R - think this code is very easy to understand:</p>
  
  <pre><code>library(dplyr)
  df = df %&gt;% 
  mutate(   #   mutate means create new column for non-r people
  my_new_column = ifelse( is.na(the_2nd_column)==TRUE &amp; is.na(the_3rd_column)==TRUE, ' abc', 'cuz')
  </code></pre>
  
  <p>how do I do this in pandas - probably dumb question with the syntax, but I have heard np.where is the equivalent of if else in R...</p>
  
  <pre><code>df['new_column'] = np.where(np.nan(....help here with a conditional....))
  </code></pre>