billing: Mention the exact type of stripe.Customers subscriptions attribute.

stubs/stripe/__init__.pyi

@@ -1,5 +1,6 @@
 import stripe.error as error
 import stripe.util as util
+from stripe.api_resources.list_object import SubscriptionListObject
 
 from typing import Optional, Any, Dict, List
 
@@ -9,7 +10,7 @@ class Customer:
     default_source: Card
     created: int
     id: str
-    subscriptions: List[Subscription]
+    subscriptions: SubscriptionListObject
 
     @staticmethod
     def retrieve(customer_id: str, expand: Optional[List[str]]) -> Customer:

stubs/stripe/api_resources/list_object/__init__.pyi

@@ -1,2 +1,8 @@
-class ListObject:
-    ...
+from stripe import Subscription
+from typing import Optional, Any, Dict, List, Iterator
+
+class SubscriptionListObject:
+    data: List[Subscription]
+
+    def __iter__(self) -> Iterator[Subscription]:
+        ...

zilencer/tests/test_stripe.py

@@ -6,7 +6,6 @@ import ujson
 from django.core import signing
 
 import stripe
-from stripe.api_resources.list_object import ListObject
 
 from zerver.lib.actions import do_deactivate_user, do_create_user, \
     do_activate_user, do_reactivate_user, activity_change_requires_seat_update