code: def to_user_agent(self):
          
  
          # Note: the order here is important as the internal metrics system
          # expects these items to be in specific locations.
          ua = ""
  
          if self.user_agent is not None:
              ua += "{user_agent} "
  
          ua += "gl-python/{python_version} "
  
          if self.grpc_version is not None:
              ua += "grpc/{grpc_version} "
  
          ua += "gax/{api_core_version} "
  
          if self.gapic_version is not None:
              ua += "gapic/{gapic_version} "
  
          if self.client_library_version is not None:
              ua += "gccl/{client_library_version} "
  
          return ua.format(**self.__dict__).strip()
docs: Returns the user-agent string for this client info.