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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def getlines(self, bufnr=None):
 """Get all lines of a buffer as a list. Args: bufnr (Optional[int]):
 A Vim buffer number, current if ``None``. Returns: List[str] """

        buf = self._vim.buffers[bufnr] if bufnr else self._vim.current.buffer
        return buf[:]