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Extending Python methods

Extending Python methods

The business logic that's coded into Python methods can also be extended. For this, Odoo borrows the mechanism that Python already provides for inherited objects to extend their parent class behavior.
As a practical example, we will extend the Library Book ISBN validation logic. The logic provided by the base Library app only validates modern 13-digit ISBNs, but some older titles might have a 10-digit ISBN. We will extend the _check_isbn() method to also validate these cases.
Add this additional method in the library_member/models/library_book.py file:
from odoo import api, fields, models


class Book(models.Model):
    _inherit = 'library.book'
    is_available = fields.Boolean('Is Available?', readonly=False)

    @api.multi
    def _check_isbn(self):
        self.ensure_one()
        digits = [int(x) for x in self.isbn if x.isdigit()]
        if len(digits) == 10:
            ponderators = [1, 2, 3, 4, 5, 6, 7, 8, 9]
            total = sum(a * b for a, b in zip(digits[:9], ponderators))
            check = total % 11
            return digits[-1] == check
        else:
            return super()._check_isbn()
To extend a method, we define it again, and at some point, can use super() to call the method's existing implementation. In our method, we check whether it is a 10-digit ISBN, and in that case, perform the missing validation logic. Otherwise, we fall back to the original ISBN checking logic that can handle the 13-digit case.


If you want to try it, or even better, write a test case, here is an example of a 10-digit ISBN: 0-571-05686-5. It is the original ISBN of William Golding's Lord of the Flies.

Note

Changes in Odoo 11 Since Odoo 11, the main Python version that's supported is Python 3 (Python 3.5 in Odoo 12). For previous Odoo versions, using Python 2, super() needed two arguments, passing the class name and self. In that case, the last statement would use super(Book, self)._check_isbn().
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