title: reshape a dataframe using pandas
body: <p>I have a .csv file like this</p>
  
  <pre><code>ID FirstName LastName  Age   FirstName   LastName   Age
  1   Sid       Than      21     Sidd         Thang   26
  2   Art       Mari      21     Arth         Mariap  28
  </code></pre>
  
  <p>When I read this inside python using pandas the column names automatically changes to FirstName_y LastName_y Age_y for all the second occurances.</p>
  
  <p>Now, I want to change the df to look like this,</p>
  
  <pre><code>Name_Key        ID   FirstName LastName   Age
  1_Sid_Than      1     Sid       Than       21
  1_Sidd_Thang    1     Sidd      Thang      26
  2_Art_Mari      2     Art       Mari       21
  2_Arth_Mariap   2     Arth      Mariap     28
  </code></pre>
  
  <p>ID is a string in my case. 
  How Can I do this using Pandas.</p>