title: Pad a column of strings in a pandas dataframe
body: <p>I have a pandas dataframe with string in a column like this</p>
  
  <pre><code> id   b
    1   this is string1
    1   this is string2
    1   this is string3
    1   this is string4
  </code></pre>
  
  <p>Now I want to remove the first character(t) from each cell of column b. I also need to add a character <code>s</code> at the beginning and end of this column. So the output should look like this</p>
  
  <pre><code> id   b
    1   shis is string1s
    1   shis is string2s
    1   shis is string3s
    1   shis is string4s
  </code></pre>
  
  <p>I know I can iterate over each row and do these operations but I was hopping there might be some efficient way of doing this. Maybe I can apply same operation on all cells of column b at once?</p>