def extractKmers(X, k=12):
    """Extract the kmers of length k of X."""

    # Length of the sequences
    len_seq = len(X[0])

    # Initialisation of the set of kmers
    k_mers = set()

    # Loop over the sequences of X
    for x_i in X:

        # Loop over the sequence
        for l in range(len_seq - k + 1):

            # Extract k_mer of x_i
            k_mer_i = x_i[l:(l + k)]

            # Update k_mers
            k_mers.update([k_mer_i])

    return list(k_mers)