old_contents: # -*- coding: utf-8 -*-
  ##############################################################################
  #
  # Copyright (c) 2013-2014 Camptocamp (http://www.camptocamp.com)
  #
  # Author : Vincent Renaville (Camptocamp)
  #
  #    This program is free software: you can redistribute it and/or modify
  #    it under the terms of the GNU Affero General Public License as
  #    published by the Free Software Foundation, either version 3 of the
  #    License, or (at your option) any later version.
  #
  #    This program is distributed in the hope that it will be useful,
  #    but WITHOUT ANY WARRANTY; without even the implied warranty of
  #    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  #    GNU Affero General Public License for more details.
  #
  #    You should have received a copy of the GNU Affero General Public License
  #    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  #
  ##############################################################################
  
  from openerp import models, fields, api
  
  
  class AccountMoveLine(models.Model):
      _inherit = "account.move.line"
  
      # We set the tax_amount readonly, because we recompute it in every case.
      tax_amount = fields.Float(readonly=True)
  
      @api.one
      def force_compute_tax_amount(self):
          if self.tax_code_id:
              self.tax_amount = self.credit - self.debit
  
      @api.model
      @api.returns('self', lambda value: value.id)
      def create(self, vals):
          record = super(AccountMoveLine, self).create(vals)
          record.force_compute_tax_amount()
          return record
  
      @api.multi
      def write(self, vals):
          result = super(AccountMoveLine, self).write(vals)
          if ('debit' in vals) or ('credit' in vals):
              self.force_compute_tax_amount()
          return result
  
new_contents: # -*- coding: utf-8 -*-
  ##############################################################################
  #
  # Copyright (c) 2013-2014 Camptocamp (http://www.camptocamp.com)
  #
  # Author : Vincent Renaville (Camptocamp)
  #
  #    This program is free software: you can redistribute it and/or modify
  #    it under the terms of the GNU Affero General Public License as
  #    published by the Free Software Foundation, either version 3 of the
  #    License, or (at your option) any later version.
  #
  #    This program is distributed in the hope that it will be useful,
  #    but WITHOUT ANY WARRANTY; without even the implied warranty of
  #    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  #    GNU Affero General Public License for more details.
  #
  #    You should have received a copy of the GNU Affero General Public License
  #    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  #
  ##############################################################################
  
  from openerp import models, fields, api
  
  
  class AccountMoveLine(models.Model):
      _inherit = "account.move.line"
  
      # We set the tax_amount readonly, because we recompute it in every case.
      tax_amount = fields.Float(readonly=True)
  
      @api.one
      def force_compute_tax_amount(self):
          if self.tax_code_id:
              self.tax_amount = self.credit - self.debit
  
      @api.cr_uid_context
      def create(self, cr, uid, vals, context=None, check=True):
          record_id = super(AccountMoveLine, self).create(cr, uid, vals,
                                                          context=context,
                                                          check=check)
          self.force_compute_tax_amount(cr, uid, [record_id], context=context)
          return record_id
  
  
      @api.cr_uid_ids_context
      def write(self, cr, uid, ids, vals, context=None, check=True,
                update_check=True):
          result = super(AccountMoveLine, self).write(cr, uid, ids, vals,
                                                      context=context,
                                                      check=check,
                                                      update_check=update_check)
  
          if ('debit' in vals) or ('credit' in vals):
              self.force_compute_tax_amount(cr, uid, ids, context=context)
          return result
  
subject: Fix signature compatibility issues for create() and write()