def subsequence(fasta_dictionary, contig_name, start, end):
    """
    Extracts a sub-sequence from `start` to `end` of `contig_name` in `fasta_dictionary`
     with headers for keys and sequences as values. `contig_name` does not contain the '>' character
    :param fasta_dictionary:
    :param contig_name:
    :param start:
    :param end:
    :return: A string representing the sub-sequence of interest
    """
    subseq = fasta_dictionary['>' + contig_name][start:end]
    return subseq
