code: def proposal(self, proposer=None, proposal_expiration=None, proposal_review=None):
          
          if not self._propbuffer:
              return self.new_proposal(
                  self.tx(), proposer, proposal_expiration, proposal_review
              )
          if proposer:
              self._propbuffer[0].set_proposer(proposer)
          if proposal_expiration:
              self._propbuffer[0].set_expiration(proposal_expiration)
          if proposal_review:
              self._propbuffer[0].set_review(proposal_review)
          return self._propbuffer[0]
docs: Return the default proposal buffer
  
              ... note:: If any parameter is set, the default proposal
                 parameters will be changed!