account_search_ruc/account_search_ruc.py

from openerp import models,fields,api

class account_invoice(models.Model):
    _name = 'account.invoice'
    _inherit = 'account.invoice'

    @api.one
    @api.depends('partner_id')
    def _partner_data(self):
        self.partner_ruc = self.partner_id.ruc

    partner_ruc = fields.Char(
        'R.U.C.',
        compute='_partner_data',
        store=True,
        search='_search_partner_ruc'
    )

    def _search_partner_ruc(self, operator, value):
        if ',' in value:
            rucs = [x.strip() for x in value.split(',') if x.strip()]
            return [('partner_ruc', 'in', rucs)]

        return [('partner_ruc', operator, value)]