title: Loading only one sheet to dataframe
body: <p>I am trying to read an excel sheet into df using pandas read_excel method. The excel file contains 6-7 different sheet. Out of it, 2-3 sheets are very huge. I only want to read one excel sheet out of the file. 
  If I copy the sheet out and read the time reduces by 90%.</p>
  
  <p>I have read that xlrd that is used by pandas always loads the whole sheet to memory. I cannot change the format of the input.  </p>
  
  <p>Can you please suggest a way to improve the performance?</p>