def start(self, stdout=subprocess.PIPE, stderr=subprocess.PIPE):
        """ Merged copy paste from the inheritance chain with modified stdout/err behaviour """
        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
Merged copy paste from the inheritance chain with modified stdout/err behaviour