I want to scrape a webpage that changes its content via a <select> tag. When I select a different option, the content of the page dynamically changes. I want to know if there is a way that I can change the option from a python script so I can get the content from all different pages of all different options in <select> tag.
I assume you use some library like urllib to do the scraping. You already know the website's content changes dynamically.  I also assume that the dynamic content uses server-side interaction. This means, using javascript (ajax) the browser requests new data from the server, based on the value from the selection). 
If so, then you could try to emulate the ajax call to the server in your web scraping library. 

First, using a browser debugging tool find out the url to the server that is being invoked.
Split the parameters parts in the ajax call
Perform the same call to lookup the options in the select tag.
How to scrape a webpage that changes content from  tag