code: def bitScoreToEValue(bitScore, dbSize, dbSequenceCount, queryLength,
                       lengthAdjustment):
      
      effectiveDbSize = (
          (dbSize - dbSequenceCount * lengthAdjustment) *
          (queryLength - lengthAdjustment)
      )
      return effectiveDbSize * (2.0 ** (-1.0 * bitScore))
docs: Convert a bit score to an e-value.
  
      @param bitScore: The C{float} bit score to convert.
      @param dbSize: The C{int} total size of the database (i.e., the sum of
          the lengths of all sequences in the BLAST database).
      @param dbSequenceCount: The C{int} number of sequences in the database.
      @param queryLength: The C{int} length of the query.
      @param lengthAdjustment: The C{int} length adjustment (BLAST XML output
          calls this the Statistics_hsp-len).
      @return: A C{float} e-value.