activating a webpage's click command from python

[Grimes, Jessica C]

How do I activate a click command on Yahoo's website from Python?    

I want to create a  program that will ask the user what stock he/she wants to look up.  The program will then extract financial data from yahoo and import it into a spreadsheet.  

My problem is that I don't know how to make the application take the user's input (the stock's ticker symbol) and place the user's input from python into the space where yahoo accepts input for a ticker symbol and activate yahoo's "Look up" click command. 

I hope I have explained my question clearly.  If my proposed method is impossible, can you suggest another approach to designing the program? 

Thank you, 

Jessica Grimes