If you want to perform all checks on lines in Odoo follow the following code:

  if 'account_id' not in vals or 'journal_id' not in vals:
            raise UserError(_("It is mandatory to specify an account and a journal to create a write-off."))
        if ('debit' in vals) ^ ('credit' in vals):
            raise UserError(_("Either pass both debit and credit or none."))
        if 'date' not in vals:
            vals['date'] = self._context.get('date_p') or time.strftime('%Y-%m-%d')
        if 'name' not in vals:
            vals['name'] = self._context.get('comment') or _('Write-Off')
        #compute the writeoff amount if not given
        if 'credit' not in vals and 'debit' not in vals:
            amount = sum([r.amount_residual for r in self])
            vals['credit'] = amount > 0 and amount or 0.0
            vals['debit'] = amount < 0 and abs(amount) or 0.0
        vals['partner_id'] = self.env['res.partner']._find_accounting_partner(self[0].partner_id).id
        company_currency = self[0].account_id.company_id.currency_id
        account_currency = self[0].account_id.currency_id or company_currency
        if 'amount_currency' not in vals and account_currency != company_currency:
            vals['currency_id'] = account_currency
            vals['amount_currency'] = sum([r.amount_residual_currency for r in self])

        # Writeoff line in the account of self
        first_line_dict = vals.copy()
        first_line_dict['account_id'] = self[0].account_id.id
        if 'analytic_account_id' in vals:
            del vals['analytic_account_id']

        # Writeoff line in specified writeoff account
        second_line_dict = vals.copy()
        second_line_dict['debit'], second_line_dict['credit'] = second_line_dict['credit'], second_line_dict['debit']
        if 'amount_currency' in vals:
            second_line_dict['amount_currency'] = -second_line_dict['amount_currency']

        # Create the move
        writeoff_move = self.env['account.move'].create({
            'journal_id': vals['journal_id'],
            'date': vals['date'],
            'state': 'draft',
            'line_ids': [(0, 0, first_line_dict), (0, 0, second_line_dict)],
        })
        writeoff_move.post()

        # Return the writeoff move.line which is to be reconciled
        return writeoff_move.line_ids.filtered(lambda r: r.account_id == self[0].account_id)

    @api.multi
    def remove_move_reconcile(self):
        """ Undo a reconciliation """
        if not self:
            return True
        rec_move_ids = self.env['account.partial.reconcile']
        for account_move_line in self:
            rec_move_ids += account_move_line.matched_debit_ids
            rec_move_ids += account_move_line.matched_credit_ids
        return rec_move_ids.unlink()
 company_ids = set()
        all_accounts = []
        partners = set()
        for line in self:
            company_ids.add(line.company_id.id)
            all_accounts.append(line.account_id)
            if (line.account_id.internal_type in ('receivable', 'payable')):
                partners.add(line.partner_id.id)
            if line.reconciled:
                raise UserError(_('You are trying to reconcile some entries that are already reconciled!'))
        if len(company_ids) > 1:
            raise UserError(_('To reconcile the entries company should be the same for all entries!'))
        if len(set(all_accounts)) > 1:
            raise UserError(_('Entries are not of the same account!'))
        if not all_accounts[0].reconcile:
            raise UserError(_('The account %s (%s) is not marked as reconciliable !') % (all_accounts[0].name, all_accounts[0].code))
        if len(partners) > 1:
            raise UserError(_('The partner has to be the same on all lines for receivable and payable accounts!'))

        #reconcile everything that can be
        remaining_moves = self.auto_reconcile_lines()

        #if writeoff_acc_id specified, then create write-off move with value the remaining amount from move in self
        if writeoff_acc_id and writeoff_journal_id and remaining_moves:
            writeoff_to_reconcile = remaining_moves._create_writeoff({'account_id': writeoff_acc_id.id, 'journal_id': writeoff_journal_id.id})
            #add writeoff line to reconcile algo and finish the reconciliation
            remaining_moves = (remaining_moves + writeoff_to_reconcile).auto_reconcile_lines()

    def _create_writeoff(self, vals):
        """ Create a writeoff move for the account.move.lines in self. If debit/credit is not specified in vals,
            the writeoff amount will be computed as the sum of amount_residual of the given recordset.

            :param vals: dict containing values suitable fot account_move_line.create(). The data in vals will
                be processed to create bot writeoff acount.move.line and their enclosing account.move.
        """
        # Check and complete vals
        if 'account_id' not in vals or 'journal_id' not in vals:
            raise UserError(_("It is mandatory to specify an account and a journal to create a write-off."))
        if ('debit' in vals) ^ ('credit' in vals):
            raise UserError(_("Either pass both debit and credit or none."))
        if 'date' not in vals:
            vals['date'] = self._context.get('date_p') or time.strftime('%Y-%m-%d')
        if 'name' not in vals:
            vals['name'] = self._context.get('comment') or _('Write-Off')
        #compute the writeoff amount if not given
        if 'credit' not in vals and 'debit' not in vals:
            amount = sum([r.amount_residual for r in self])
            vals['credit'] = amount > 0 and amount or 0.0
            vals['debit'] = amount < 0 and abs(amount) or 0.0
        vals['partner_id'] = self.env['res.partner']._find_accounting_partner(self[0].partner_id).id
        company_currency = self[0].account_id.company_id.currency_id
        account_currency = self[0].account_id.currency_id or company_currency
        if 'amount_currency' not in vals and account_currency != company_currency:
            vals['currency_id'] = account_currency
            vals['amount_currency'] = sum([r.amount_residual_currency for r in self])

        # Writeoff line in the account of self
        first_line_dict = vals.copy()
        first_line_dict['account_id'] = self[0].account_id.id
        if 'analytic_account_id' in vals:
            del vals['analytic_account_id']

        # Writeoff line in specified writeoff account
        second_line_dict = vals.copy()
        second_line_dict['debit'], second_line_dict['credit'] = second_line_dict['credit'], second_line_dict['debit']
        if 'amount_currency' in vals:
            second_line_dict['amount_currency'] = -second_line_dict['amount_currency']