'Returns a string that will be used to group account.invoice.tax sharing the same properties'

def get_grouping_key(self, invoice_tax_val):

    self.ensure_one()
    return ((((str(invoice_tax_val['tax_id']) + '-') + str(invoice_tax_val['account_id'])) + '-') + str(invoice_tax_val['account_analytic_id']))
