@classmethod
def from_file_and_offsets(cls, file, hdr_offset, data_offset, disk_length):
    """Instantiate a Rec object from the file object and the header and
    data offsets. The headers are read in, and also the record object
    is ready for calling get_data().

        """
    c = file._c_interface
    int_hdr, real_hdr = c.read_header(file.fd, hdr_offset, file.
        byte_ordering, file.word_size)
    return cls(int_hdr, real_hdr, hdr_offset, data_offset, disk_length,
        file=file)
