<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def getline(self, lnum=None):
 """Get a line from the current buffer. Args: lnum (Optional[str]):
 Number of the line to get, current if ``None``. Todo: - Give this more behavior of Vim ``getline()``? - ``buffer[index]`` is zero-based, this is probably too confusing """

        return self._vim.current.buffer[lnum] if lnum else self._vim.current.line