How to use the localstripe.resources.SubscriptionItem function in localstripe

if 'subscription_id' in request.match_info:
            data['subscription_id'] = request.match_info['subscription_id']
        expand = data.pop('expand', None)
        return json_response(func(**data)._export(expand=expand))
    return f


# Extra routes must be added *before* regular routes, because otherwise
# `/invoices/upcoming` would fall into `/invoices/{id}`.
for method, url, func in extra_apis:
    app.router.add_route(method, url, api_extra(func, url))


for cls in (Charge, Coupon, Customer, Event, Invoice, InvoiceItem,
            PaymentIntent, PaymentMethod, Plan, Product, Refund, SetupIntent,
            Source, Subscription, SubscriptionItem, TaxRate, Token):
    for method, url, func in (
            ('POST', '/v1/' + cls.object + 's', api_create),
            ('GET', '/v1/' + cls.object + 's/{id}', api_retrieve),
            ('POST', '/v1/' + cls.object + 's/{id}', api_update),
            ('DELETE', '/v1/' + cls.object + 's/{id}', api_delete),
            ('GET', '/v1/' + cls.object + 's', api_list_all)):
        app.router.add_route(method, url, func(cls, url))


def localstripe_js(request):
    path = os.path.dirname(os.path.realpath(__file__)) + '/localstripe-v3.js'
    with open(path) as f:
        return web.Response(text=f.read(),
                            content_type='application/javascript')

def __init__(self, item):
        try:
            assert isinstance(item, (InvoiceItem, SubscriptionItem))
        except AssertionError:
            raise UserError(400, 'Bad request')

        # All exceptions must be raised before this point.
        super().__init__()

        self.type = \
            'invoiceitem' if isinstance(item, InvoiceItem) else 'subscription'

        if self.type == 'subscription':
            self.subscription_item = item.id
            self.subscription = item._subscription
            self.plan = item.plan
            self.proration = False
            self.currency = item.plan.currency
            self.description = item.plan.name

for previous_invoice in previous._list:
                    previous_tax_rates = [tr.id for tr in (
                        previous_invoice.lines._list[0].tax_rates or [])]
                    InvoiceItem(amount=- previous_invoice.subtotal,
                                currency=previous_invoice.currency,
                                proration=True,
                                description='Unused time',
                                subscription=self.id,
                                plan=old_plan.id,
                                tax_rates=previous_tax_rates,
                                customer=self.customer)

            elif self.items._list[0].tax_rates != items[0]['tax_rates']:
                self.items = List('/v1/subscription_items?subscription=' +
                                  self.id)
                item = SubscriptionItem(subscription=self.id,
                                        plan=items[0]['plan'],
                                        quantity=items[0]['quantity'],
                                        tax_rates=items[0]['tax_rates'])
                self.items._list.append(item)

        if tax_percent is not None:
            self.tax_percent = tax_percent
        if default_tax_rates is not None:
            self.default_tax_rates = [TaxRate._api_retrieve(tr)
                                      for tr in default_tax_rates]

        if trial_end is not None:
            self.trial_end = trial_end

        if cancel_at_period_end is not None:
            self.cancel_at_period_end = cancel_at_period_end

[tr.id for tr in current_subscription.default_tax_rates]

        invoice_items = []
        items = subscription_items or \
            (current_subscription and current_subscription.items._list) or []
        for si in items:
            if subscription_items is not None:
                plan = Plan._api_retrieve(si['plan'])
                quantity = si.get('quantity', 1)
                tax_rates = si['tax_rates']
            else:
                plan = si.plan
                quantity = si.quantity
                tax_rates = [tr.id for tr in (si.tax_rates or [])]
            invoice_items.append(
                SubscriptionItem(subscription=subscription,
                                 plan=plan.id,
                                 quantity=quantity,
                                 tax_rates=tax_rates))

        if tax_percent is None:
            if subscription_tax_percent is not None:
                tax_percent = subscription_tax_percent
            elif current_subscription:
                tax_percent = current_subscription.tax_percent

        date = int(time.time())  # now
        if current_subscription:
            date = current_subscription.current_period_end

        if not simulation and not current_subscription:
            raise UserError(404, 'No upcoming invoices for customer')

self.ended_at = None
        self.quantity = items[0]['quantity']
        self.status = 'incomplete'
        self.trial_end = trial_end
        self.trial_start = None
        self.trial_period_days = trial_period_days
        self.latest_invoice = None
        self.start_date = backdate_start_date or int(time.time())
        self.billing_cycle_anchor = billing_cycle_anchor
        self._enable_incomplete_payments = (
            enable_incomplete_payments and
            payment_behavior != 'error_if_incomplete')

        self.items = List('/v1/subscription_items?subscription=' + self.id)
        self.items._list.append(
            SubscriptionItem(
                subscription=self.id,
                plan=items[0]['plan'],
                quantity=items[0]['quantity'],
                tax_rates=items[0]['tax_rates']))

        create_an_invoice = \
            self.trial_end is None and self.trial_period_days is None
        if create_an_invoice:
            self._create_invoice()

        schedule_webhook(Event('customer.subscription.created', self))