title: Return the column name(s) for a specific value in a pandas dataframe
body: <p>where I have found this option in other languages such as R or SQL but I am not quite sure how to go about this in Pandas.</p>
  
  <p>So I have a file with 1262 columns and 1 row and need the column headers to return for every time that a specific value appears. </p>
  
  <p>Say for example this test dataframe:</p>
  
  <pre><code>Date               col1    col2    col3    col4    col5    col6    col7 
  01/01/2016 00:00   37.04   36.57   35.77   37.56   36.79   35.90   38.15 
  </code></pre>
  
  <p>And I need to locate the column name for e.g. where value = 38.15. What is the best way of doing so?</p>
  
  <p>Thanks</p>