Stores information about one hsp in an alignment hit.

Members:

- score           BLAST score of hit.  (float)
- bits            Number of bits for that score.  (float)
- expect          Expect value.  (float)
- num_alignments  Number of alignments for same subject.  (int)
- identities      Number of identities (int) if using the XML parser.
  Tuple of number of identities/total aligned (int, int)
  if using the (obsolete) plain text parser.
- positives       Number of positives (int) if using the XML parser.
  Tuple of number of positives/total aligned (int, int)
  if using the (obsolete) plain text parser.
- gaps            Number of gaps (int) if using the XML parser.
  Tuple of number of gaps/total aligned (int, int) if
  using the (obsolete) plain text parser.
- align_length    Length of the alignment. (int)
- strand          Tuple of (query, target) strand.
- frame           Tuple of 1 or 2 frame shifts, depending on the flavor.

- query           The query sequence.
- query_start     The start residue for the query sequence.  (1-based)
- query_end       The end residue for the query sequence.  (1-based)
- match           The match sequence.
- sbjct           The sbjct sequence.
- sbjct_start     The start residue for the sbjct sequence.  (1-based)
- sbjct_end       The end residue for the sbjct sequence.  (1-based)

Not all flavors of BLAST return values for every attribute::

          score     expect     identities   positives    strand  frame
BLASTP     X          X            X            X
BLASTN     X          X            X            X          X
BLASTX     X          X            X            X                  X
TBLASTN    X          X            X            X                  X
TBLASTX    X          X            X            X                 X/X

Note: for BLASTX, the query sequence is shown as a protein sequence, but the numbering is based on the nucleotides. Thus, the numbering is 3x larger than the number of amino acid residues. A similar effect can be seen for the sbjct sequence in TBLASTN, and for both sequences in TBLASTX.

Also, for negative frames, the sequence numbering starts from query_start and counts down.