def to_dictionary(pw, print_list):
    """
    - convert list of comparisons to dictionary
    - print list of pidents (if requested) to stderr
    """
    pairs = {}
    for p in pw:
        a, b, pident = p
        if a not in pairs:
            pairs[a] = {a: '-'}
        if b not in pairs:
            pairs[b] = {b: '-'}
        pairs[a][b] = pident
        pairs[b][a] = pident
        if print_list is True:
            A, B = a.split('>')[1], b.split('>')[1]
            print('\t'.join([str(i) for i in [A, B, pident]]), file=sys.stderr)
            print('\t'.join([str(i) for i in [B, A, pident]]), file=sys.stderr)
    return pairs