title: Pandas - find index of value anywhere in DataFrame
body: <p>I'm new to Python &amp; Pandas. </p>
  
  <p>I want to find the index of a certain value (let's say <code>security_id</code>) in my pandas dataframe, because that is where the columns start. 
  (There is an unknown number of rows with irrelevant data above the columns, as well as a number of empty 'columns' on the left side.)</p>
  
  <p>As far as I see, the <a href="http://pandas.pydata.org/pandas-docs/version/0.17.0/generated/pandas.DataFrame.isin.html" rel="noreferrer">isin</a> method only returns a boolean on whether the value exists, not its index.</p>
  
  <p>How do I find the index of this value?</p>