code: def start(self, stdout=subprocess.PIPE, stderr=subprocess.PIPE):
          
          if self.pre_start_check():
              # Some other executor (or process) is running with same config:
              raise AlreadyRunning(self)
  
          if self.process is None:
              command = self.command
              if not self._shell:
                  command = self.command_parts
  
              env = os.environ.copy()
              env[ENV_UUID] = self._uuid
              popen_kwargs = {
                  'shell': self._shell,
                  'stdin': subprocess.PIPE,
                  'stdout': stdout,
                  'stderr': stderr,
                  'universal_newlines': True,
                  'env': env,
              }
              if platform.system() != 'Windows':
                  popen_kwargs['preexec_fn'] = os.setsid
              self.process = subprocess.Popen(
                  command,
                  **popen_kwargs,
              )
  
          self._set_timeout()
  
          self.wait_for(self.check_subprocess)
          return self
docs: Merged copy paste from the inheritance chain with modified stdout/err behaviour