'Read a segment of data from a file.
Only needs to be implemented for readers that support
``preload=False``.
Parameters
data : ndarray, shape (len(idx), stop - start + 1)
The data array. Should be modified inplace.
idx : ndarray | slice
The requested channel indices.
fi : int
The file index that must be read from.
start : int
The start sample in the given file.
stop : int
The stop sample in the given file (inclusive).
cals : ndarray, shape (len(idx), 1)
Channel calibrations (already sub-indexed).
mult : ndarray, shape (len(idx), len(info[\'chs\']) | None
The compensation + projection + cals matrix, if applicable.'

def _read_segment_file(self, data, idx, fi, start, stop, cals, mult):

    raise NotImplementedError
