<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def cat(self, numlines=None):
 """Return a list of lines output by this service."""

        if len(self.titles) == 1:
            lines = self.lines()
            if numlines is not None:
                lines = lines[len(lines)-numlines:]
            log("\n".join(lines))
        else:
            lines = [self._printtuple(line[0], line[1]) for line in self.lines()]
            if numlines is not None:
                lines = lines[len(lines)-numlines:]
            log("".join(lines))