title: pandas dataframe search with contains and get the row number
body: <p>In a dataframe , I want to search for a string in on the first column and on finding that string , I would like to get the row number and assign it as a variable,</p>
  <p>my dataframe looks something like this</p>
  <pre><code>df = pd.DataFrame({'A': ['xx', '--- bios ---', 'yy', 'zz', '--- os ---'],'B': ['rat', '', 'winter', 'host','']})
  </code></pre>
  <p>I am trying to get row number of the string and assign it to a variable ,as below</p>
  <pre><code>var = df.iloc[:,0].str.contains('--- bios ---').index
  </code></pre>
  <p>where --- bios --- is the search word and I am trying to get the index</p>
  <p>but I am not getting the desired output, output i am expecting is 4 which is the row number</p>