capture.py 文件源码

def start(self):
        try:
            os.fstat(self._savefd)
        except OSError:
            raise ValueError("saved filedescriptor not valid, "
                "did you call start() twice?")
        if self.targetfd == 0 and not self.tmpfile:
            fd = os.open(devnullpath, os.O_RDONLY)
            os.dup2(fd, 0)
            os.close(fd)
            if hasattr(self, '_oldsys'):
                setattr(sys, patchsysdict[self.targetfd], DontReadFromInput())
        else:
            os.dup2(self.tmpfile.fileno(), self.targetfd)
            if hasattr(self, '_oldsys'):
                setattr(sys, patchsysdict[self.targetfd], self.tmpfile)