title: How to identity non-empty columns in pandas dataframe?
body: <p>I'm processing a dataset with around 2000 columns and I noticed many of them are empty. I want to know specifically how many of them are empty and how many are not. I use the following code:</p>
  
  <pre><code>df.isnull().sum()
  </code></pre>
  
  <p>I will get the number of empty rows in each columns. However, given I'm investigating about 2000 columns with 7593 rows, the output in IPython looks like the following:</p>
  
  <pre><code>FEMALE_DEATH_YR3_RT              7593
  FEMALE_COMP_ORIG_YR3_RT          7593
  PELL_COMP_4YR_TRANS_YR3_RT       7593
  PELL_COMP_2YR_TRANS_YR3_RT       7593
                               ... 
  FIRSTGEN_YR4_N                   7593
  NOT1STGEN_YR4_N                  7593
  </code></pre>
  
  <p>It doesn't show all the columns because it has too many columns. Thus it makes it very difficult to tell how many columns are all empty and how any are not.
  I wonder is there anyway to allow me to identify the non-empty columns quickly? Thanks!</p>