code: def tanimoto_coeff(self, src, tar, qval=2):
          
          coeff = self.sim(src, tar, qval)
          if coeff != 0:
              return log(coeff, 2)
  
          return float('-inf')
docs: Return the Tanimoto distance between two strings.
  
          Tanimoto distance :cite:`Tanimoto:1958` is
          :math:`-log_{2} sim_{Tanimoto}(X, Y)`.
  
          Parameters
          ----------
          src : str
              Source string (or QGrams/Counter objects) for comparison
          tar : str
              Target string (or QGrams/Counter objects) for comparison
          qval : int
              The length of each q-gram; 0 for non-q-gram version
  
          Returns
          -------
          float
              Tanimoto distance
  
          Examples
          --------
          >>> cmp = Jaccard()
          >>> cmp.tanimoto_coeff('cat', 'hat')
          -1.5849625007211563
          >>> cmp.tanimoto_coeff('Niall', 'Neil')
          -2.1699250014423126
          >>> cmp.tanimoto_coeff('aluminum', 'Catalan')
          -4.0
          >>> cmp.tanimoto_coeff('ATCG', 'TAGC')
          -inf