code: def reduce_by(self, package_request):
          
          if self.pr:
              reqstr = _short_req_str(package_request)
              self.pr.passive("reducing %s wrt %s...", self, reqstr)
  
          if self.solver.optimised:
              if package_request in self.been_reduced_by:
                  return (self, [])
  
          if (package_request.range is None) or \
                  (package_request.name not in self.fam_requires):
              return (self, [])
  
          with self.solver.timed(self.solver.reduction_time):
              return self._reduce_by(package_request)
docs: Remove variants whos dependencies conflict with the given package
          request.
  
          Returns:
              (VariantSlice, [Reduction]) tuple, where slice may be None if all
              variants were reduced.