You should be inheriting from the payslip_report class in hr_payroll/report/report_payslip.py.  First, before the class definition you should put: from hr_payroll.report import report_payslip.  Then the class definition should be class payslip_report(report_payslip.payslip_report).  This way, you chain your inheritance (this is python inheritance, not Odoo ORM inheritance) through the class that provides the get_payslip_lines method.

Also don't forget to re-register your report with the new parser.  At the end of the py file, add the following line: report_sxw.report_sxw('report.payslip', 'hr.payslip', 'hr_payroll/report/report_payslip.rml', parser=payslip_report) adjust the information as necessary.

Hi friends:

I solved it in the following way:

I wanted to increase a column in trial balance, this column show before account balance to period or date chosen by the user in the wizard of trial balance.


First Inherit template of tria balance:

<template id="report_trialbalance_saldo_anterior" inherit_id="account.report_trialbalance">
            <xpath expr="//table[@class='table table-condensed']" position="replace">
                <table class="table table-condensed">
                    <thead>
                        <tr>
                            <th>Code</th>
                            <th>Account</th>
                            <th>Saldo Anterior</th>
                            <th class="text-right">Debit</th>
                            <th class="text-right">Credit</th>
                            <th class="text-right">Balance</th>
                        </tr>
                    </thead>
                    <tbody>
                        <tr t-foreach="lines_comprobacion(data['form'])" t-as="childrenaccount">
                            <t t-if="childrenaccount['type'] == 'view'">
                                <t t-set="style" t-value="'font-weight:bold;'"/>
                            </t>
                            <t t-if="childrenaccount['type'] != 'view'">
                                <t t-set="style" t-value="'font-weight:normal;'"/>
                            </t>
                            <td>
                                <span t-att-style="style" t-esc="childrenaccount['code']"/>                                   
                            </td>
                            <td>
                                <span style="color: white;" t-esc="'.' * (childrenaccount['level'] - 1)"/>
                                <span t-att-style="style" t-esc="childrenaccount['name']"/>
                            </td>
                            <td class="text-right">
                                 <span t-att-style="style" t-esc="childrenaccount['sal_ant']" />
                            </td>
                            <td class="text-right">
                                 <span t-att-style="style" t-esc="childrenaccount['debit']"/>
                            </td>
                            <td class="text-right">
                                <span t-att-style="style" t-esc="childrenaccount['credit']"/>
                            </td>
                            <td class="text-right">
                                <span t-att-style="style" t-esc="formatLang(childrenaccount['balance'], currency_obj=res_company.currency_id)"/>
                            </td>
                        </tr>
                    </tbody>
                </table>          
            </xpath>

        </template>

And the .py in my module is:


import time

from openerp.osv import osv from openerp.report import report_sxw from openerp.addons.account.report.common_report_header import common_report_header from openerp.addons.account.report.account_balance import account_balance from datetime import datetime, timedelta

class account_balance_comprobacion(report_sxw.rml_parse, common_report_header):

    def __init__(self, cr, uid, name, context=None):
        super(account_balance_comprobacion, self).__init__(cr, uid, name, context=context)
        self.sum_debit = 0.00
        self.sum_credit = 0.00
        self.date_lst = []
        self.date_lst_string = ''
        self.result_acc = []
        self.localcontext.update({
            'time': time,
            'lines_comprobacion': self.lines_comprobacion,
            'sum_debit': self._sum_debit,
            'sum_credit': self._sum_credit,
            'get_fiscalyear':self._get_fiscalyear,
            'get_filter': self._get_filter,
            'get_start_period': self.get_start_period,
            'get_end_period': self.get_end_period ,
            'get_account': self._get_account,
            'get_journal': self._get_journal,
            'get_start_date':self._get_start_date,
            'get_end_date':self._get_end_date,
            'get_target_move': self._get_target_move,
        })
        self.context = context


    def lines_comprobacion(self, form, ids=None, done=None):

        #NEW METHOD THAT INCREASES FUNCTIONALITY


class report_trialbalance_comprobacion(osv.AbstractModel):  
    _name = 'report.account.report_trialbalance'
    _inherit = 'report.abstract_report'
    _template = 'account.report_trialbalance'
    _wrapped_report_class = account_balance_comprobacion


That was all i hope it helps

Regards.

I write a more extensive explanation of qweb report parsers at:

https://www.odoo.com/es_ES/forum/help-1/question/how-to-define-a-custom-methods-functions-to-be-used-in-a-qweb-report-how-to-define-and-use-a-report-parser-92244