Hi,

In Odoo v10 use _get_report_from_name instead report_action.

e.g:

@api.model
def render_html(self, docids, data=None):
    report_obj = self.env['report']
    report = report_obj._get_report_from_name('de_partner_statement.partner_ledger_pdf')
    docargs = {

        'doc_ids': docids,
        'doc_model': report.model,
        'docs': self,
        'result': {...}
    }
    return report_obj.render('de_partner_statement.partner_ledger_pdf', docargs)

Best regards!