code: def b(self, number):
          
          if number < 0:
              self._b = 0
          elif number > 1:
              self._b = 1
          else:
              self._b = number
docs: A parameter to tune the amount of field length normalisation that is
          applied when calculating relevance scores.
  
          A value of 0 will completely disable any normalisation and a value of 1
          will fully normalise field lengths. The default is 0.75. Values of b
          will be clamped to the range 0 - 1.