Note:
When you load the data from example_seq.txt, your data will be delimted with newlines. You need to remove these before you can process using regular expressions, because Regular expressions only work on a line by ine basis.
Use: .replace('\n','')
Example:
f = open('example_seq.txt')
data = f.read().replace('\n','')

ALSO:
Note to solve the last Homework problem, using a one liner, you'll need to use look ahead assertations (?= R)
See the re module python documentation for more information.

John