code: def _build_one_legacy(self, req, tempd, python_tag=None):
          
          base_args = self._base_setup_args(req)
  
          spin_message = 'Building wheel for %s (setup.py)' % (req.name,)
          with open_spinner(spin_message) as spinner:
              logger.debug('Destination directory: %s', tempd)
              wheel_args = base_args + ['bdist_wheel', '-d', tempd] \
                  + self.build_options
  
              if python_tag is not None:
                  wheel_args += ["--python-tag", python_tag]
  
              try:
                  output = call_subprocess(wheel_args, cwd=req.setup_py_dir,
                                           show_stdout=False, spinner=spinner)
              except Exception:
                  spinner.finish("error")
                  logger.error('Failed building wheel for %s', req.name)
                  return None
              names = os.listdir(tempd)
              wheel_path = get_legacy_build_wheel_path(
                  names=names,
                  temp_dir=tempd,
                  req=req,
                  command_args=wheel_args,
                  command_output=output,
              )
              return wheel_path
docs: Build one InstallRequirement using the "legacy" build process.
  
          Returns path to wheel if successfully built. Otherwise, returns None.