def kmer_counts(sequence, k=4):
    """Kmer counting function
    Inputs:
        - DNA Sequence (string) (Mandatory)
        - kmer size (int) (default=4)
    Output:
        - Dictionary that holds unique kmer (key) and occurences
    """
    kmers = {}
    for i in range(len(sequence) - k + 1):
       kmer = sequence[i:i+k]
       if kmer in kmers:
          kmers[kmer] += 1
       else:
          kmers[kmer] = 1
    return kmers
    # Uncomment when to print kmer and counts