<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def wait(self):
 """ waits for the running command to finish. this is called on all running commands, eventually, except for ones that run in the background """

        if not self._process_completed:
            self._process_completed = True

            exit_code = self.process.wait()
            if self.process.timed_out:
                # if we timed out, our exit code represents a signal, which is
                # negative, so let's make it positive to store in our
                # TimeoutException
                raise TimeoutException(-exit_code)

            else:
                self.handle_command_exit_code(exit_code)
        
                # if an iterable command is using an instance of OProc for its stdin,
                # wait on it.  the process is probably set to "piped", which means it
                # won't be waited on, which means exceptions won't propagate up to the
                # main thread.  this allows them to bubble up
                if self.process._stdin_process:
                    self.process._stdin_process.command.wait()

        self.log.info("process completed")
        return self