>>> import HW4
>>> sequence1 = 'ATTAG'
>>> sequence2 = 'ATAG'
>>> alignment,score = HW4.align(sequence1, sequence2, mismatch_penalty, gap_penalty)
# your align method receives two sequences (strings), which you can 
# assume are upper-case strings over the alphabet {A,C,G,T}.
# mismatch_penalty is the penalty assigned to a mismatch between 
# two letters
# gap_penalty is the penalty assigned to a gap
# the return value is a tuple whose first element is the optimal 
# alignment, and its second element is the score of the alignment.
# the alignment is formatted as a pair of strings:
>>> print alignment
('ATTAG', 'AT-AG'