def __init__(self, fileobj, start_byte, chunk_size, full_file_size,
                 callback=None, enable_callback=True):
        self._fileobj = fileobj
        self._start_byte = start_byte
        self._size = self._calculate_file_size(
            self._fileobj, requested_size=chunk_size,
            start_byte=start_byte, actual_file_size=full_file_size)
        self._fileobj.seek(self._start_byte)
        self._amount_read = 0
        self._callback = callback
        self._callback_enabled = enable_callback
Given a file object shown below::
dataset/ETHPy150Open boto/boto3/boto3/s3/transfer.py/ReadFileChunk.__init__