code: def load_pyproject_toml(self):
          # type: () -> None
          
          pep517_data = load_pyproject_toml(
              self.use_pep517,
              self.pyproject_toml,
              self.setup_py,
              str(self)
          )
  
          if pep517_data is None:
              self.use_pep517 = False
          else:
              self.use_pep517 = True
              requires, backend, check = pep517_data
              self.requirements_to_check = check
              self.pyproject_requires = requires
              self.pep517_backend = Pep517HookCaller(self.setup_py_dir, backend)
  
              # Use a custom function to call subprocesses
              self.spin_message = ""
  
              def runner(cmd, cwd=None, extra_environ=None):
                  with open_spinner(self.spin_message) as spinner:
                      call_subprocess(
                          cmd,
                          cwd=cwd,
                          extra_environ=extra_environ,
                          show_stdout=False,
                          spinner=spinner
                      )
                  self.spin_message = ""
  
              self.pep517_backend._subprocess_runner = runner
docs: Load the pyproject.toml file.
  
          After calling this routine, all of the attributes related to PEP 517
          processing for this requirement have been set. In particular, the
          use_pep517 attribute can be used to determine whether we should
          follow the PEP 517 or legacy (setup.py) code path.