# reverse_seq.py
# Author: Sami Khuri
# Last updated: January 16, 2016
# Purpose: To construct the reverse of a given DNA sequence 
# Program uses python built-in functions list(), reverse(), and join() 
# Notes: list() converst a string to a list
#        reverse() revereses elements of a list
#        join() converts a list to a string

def reverse_sequence(s): 
    """Return the sequence string in reverse order.""" 
   
    # converting string to list so as to use reverse()
    letters = list(s) 
   
    # reverse() reverses lists
    letters.reverse() 
   
    # converting list back to string
    return ''.join(letters)
      

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