Reads a line from the device.

        :param timeout: read timeout
        :type timeout: float
        :param purge_buffer: Indicates whether to purge the buffer prior to
                             reading.
        :type purge_buffer: bool

        :returns: line that was read
        :raises: :py:class:`~alarmdecoder.util.CommError`, :py:class:`~alarmdecoder.util.TimeoutError`

def read_line(self, timeout=0.0, purge_buffer=False):
        """
        Reads a line from the device.

        :param timeout: read timeout
        :type timeout: float
        :param purge_buffer: Indicates whether to purge the buffer prior to
                             reading.
        :type purge_buffer: bool

        :returns: line that was read
        :raises: :py:class:`~alarmdecoder.util.CommError`, :py:class:`~alarmdecoder.util.TimeoutError`
        """

        def timeout_event():
            """Handles read timeout event"""
            timeout_event.reading = False
        timeout_event.reading = True

        if purge_buffer:
            self._buffer = b''

        got_line, ret = False, None

        timer = threading.Timer(timeout, timeout_event)
        if timeout > 0:
            timer.start()

        try:
            while timeout_event.reading:
                buf = self._device.read_data(1)

                if buf != b'':
                    ub = bytes_hack(buf)

                    self._buffer += ub

                    if ub == b"\n":
                        self._buffer = self._buffer.rstrip(b"\r\n")

                        if len(self._buffer) > 0:
                            got_line = True
                            break
                else:
                    time.sleep(0.01)

        except (usb.core.USBError, FtdiError) as err:
            raise CommError('Error reading from device: {0}'.format(str(err)), err)

        else:
            if got_line:
                ret, self._buffer = self._buffer, b''

                self.on_read(data=ret)

            else:
                raise TimeoutError('Timeout while waiting for line terminator.')

        finally:
            timer.cancel()

        return ret