library/library_member/models/library_models.py

from odoo import fields, models

class Book(models.Model):
    _inherit = 'library.book'
    is_available = fields.Boolean('Is Available?')
    isbn = fields.Char(help="Use a valid ISBN-13 or ISBN-10.")
    publisher_id = fields.Many2one(index=True)


class Member(models.Model):
    _name = 'library.member'
    _description = 'Library Member'
    card_number = fields.Char()
    partner_id = fields.Many2one(
        'res.partner',
        delegate=True,
        ondelete='cascade',
        required=True)