title: Pandas data frame : how to check all value of last row if it is non zero
body: <p>i want to check last row's all value if it is non-zero,if it is non zero then give me column name.</p>
  <pre><code>df = pd.DataFrame({'A': [1,2,-2,0,0], 'B': [0, 0, 0, 3, -2], 'C' : [0, 0, -2, 4, 0], 'D': [0, 0, 0, 1, 0]} ) 
  </code></pre>