'Constructor.
Args:
filename: the name of the file to read as string.
buffer_size: buffer read size to use as int.'

def __init__(self, filename, buffer_size=_DEFAULT_BUFFER_SIZE):

    self._filename = filename
    self._position = 0
    self._buffer = ''
    self._buffer_pos = 0
    self._buffer_size = buffer_size
    self._eof = False
