Python - dos puntos

kmer = genome[i:i+k]

# Open the input text file.

f = open('problem001.txt', 'r')

myDictionary = {}

# First line contains the string Text

genome = f.readline().rstrip('\n')

# Second line contains k

k = int(f.readline().rstrip('\n'))

f.close()

# Number of characters in the string

numChars = len(genome)

# Step through the string 1 char at a time and substring out each k characters

for i in range (0, numChars - k + 1):

    kmer = genome[i:i+k]

    if kmer in myDictionary:

        myDictionary[kmer] += 1

    else:

        myDictionary[kmer] = 1

maxValue = 0

answer = ''

# Sort the keys in the dictionary

for w in sorted(myDictionary, key=myDictionary.get, reverse=True):

    if myDictionary[w] >= maxValue:

        maxValue = myDictionary[w]

        answer += w + ' '

        print w, myDictionary[w]

print 'answer'

print answer

variable="casa"

variable[0] # hace referencia al indice 0, que es el primer valor de la variable... devuelve "c"

variable[0:2] # hace referencia al indice 0 hasta el 2... devuelve "ca"