# draft_reverse_complement.py
# Author: Sami Khuri
# Last updated: February 13, 2016
# Purpose: To construct the reverse complement of a given DNA sequence 
# Program uses dictionary and 
#         built-in python functions: list(), join() and reverse(), and
#         user-defined complement(), reverse_seq(), and reverse_comp()

def complement(s): 
    """Return the complementary sequence string of s.""" 
    basecomplement = {'A': 'T', 'C': 'G', 'G': 'C', 'T': 'A'} 
    letters = XXXXXXXXXX   # Convert s into a list 
    
    letters = [basecomplement[XXXXXXXXXX] for base in letters] 
    return ''.join(letters)  # Convert letters into a sequence of characters

def reverse_seq(s): 
    """Return the sequence string in reverse order.""" 
    letters = XXXXXXXXXX   # Convert s into a list 
    letters.reverse() 
    return ''.join(XXXXXXXXXX)  # Convert list into a sequence of characters

def reverse_comp(s): 
    """Return the reverse complement of DNA sequence s.""" 
    comp = XXXXXXXXXX 		# Find the complement of s
    revcomp = XXXXXXXXXX(comp)  	# Now reverse the complement of s
    return revcomp
      

dna_seq = 'CCGGAAGAGCTTACTTAG' 
print "Given DNA sequence:\t", dna_seq        
print "Its reverse complement:\t", reverse_comp(dna_seq)