def get_complement(string):
    """returns a complementary DNA sequence, e.g. GCTA for TAGC. Mind the sequence inversion!"""
    string=string.replace('G','1')
    string=string.replace('A','2')
    string=string.replace('T','3')
    string=string.replace('C','4')
    string=string.replace('1','C')
    string=string.replace('2','T')
    string=string.replace('3','A')
    string=string.replace('4','G')
    string=string.replace('X','Z')#for 'blank' sticky ends and cinnamate
    return string[::-1]