class example_report(models.AbstractModel):
    _name = 'report.module_name.report_my_custom_report'
    @api.multi
    def render_html(self,data=None):
        report_obj = self.env['report']
        report = report_obj._get_report_from_name('module_name.report_my_custom_report')

        # your report data structure goes in data_array
        data_array = []
        docargs = {
            'hold_data_array':data_array,
        }
        # here we will pass the report data into our report template
        return report_obj.render('module_name.report_my_custom_report', docargs)