from pylab import *

sim_list = []


def DNA_similar(input_dna):
    for n in input_dna:
        if sim_list and sim_list[-1][0] == n:
            sim_list[-1] = (sim_list[-1] + n)
        else:
            sim_list.append(n)
    return sim_list


dna = "AAGCCTAAATTCGGG"

print(DNA_similar(dna))