python: Convert assignment type annotations to Python 3.6 style.

This commit was split by tabbott; this piece covers the vast majority
of files in Zulip, but excludes scripts/, tools/, and puppet/ to help
ensure we at least show the right error messages for Xenial systems.

We can likely further refine the remaining pieces with some testing.

Generated by com2ann, with whitespace fixes and various manual fixes
for runtime issues:

-    invoiced_through: Optional[LicenseLedger] = models.ForeignKey(
+    invoiced_through: Optional["LicenseLedger"] = models.ForeignKey(

-_apns_client: Optional[APNsClient] = None
+_apns_client: Optional["APNsClient"] = None

-    notifications_stream: Optional[Stream] = models.ForeignKey('Stream', related_name='+', null=True, blank=True, on_delete=CASCADE)
-    signup_notifications_stream: Optional[Stream] = models.ForeignKey('Stream', related_name='+', null=True, blank=True, on_delete=CASCADE)
+    notifications_stream: Optional["Stream"] = models.ForeignKey('Stream', related_name='+', null=True, blank=True, on_delete=CASCADE)
+    signup_notifications_stream: Optional["Stream"] = models.ForeignKey('Stream', related_name='+', null=True, blank=True, on_delete=CASCADE)

-    author: Optional[UserProfile] = models.ForeignKey('UserProfile', blank=True, null=True, on_delete=CASCADE)
+    author: Optional["UserProfile"] = models.ForeignKey('UserProfile', blank=True, null=True, on_delete=CASCADE)

-    bot_owner: Optional[UserProfile] = models.ForeignKey('self', null=True, on_delete=models.SET_NULL)
+    bot_owner: Optional["UserProfile"] = models.ForeignKey('self', null=True, on_delete=models.SET_NULL)

-    default_sending_stream: Optional[Stream] = models.ForeignKey('zerver.Stream', null=True, related_name='+', on_delete=CASCADE)
-    default_events_register_stream: Optional[Stream] = models.ForeignKey('zerver.Stream', null=True, related_name='+', on_delete=CASCADE)
+    default_sending_stream: Optional["Stream"] = models.ForeignKey('zerver.Stream', null=True, related_name='+', on_delete=CASCADE)
+    default_events_register_stream: Optional["Stream"] = models.ForeignKey('zerver.Stream', null=True, related_name='+', on_delete=CASCADE)

-descriptors_by_handler_id: Dict[int, ClientDescriptor] = {}
+descriptors_by_handler_id: Dict[int, "ClientDescriptor"] = {}

-worker_classes: Dict[str, Type[QueueProcessingWorker]] = {}
-queues: Dict[str, Dict[str, Type[QueueProcessingWorker]]] = {}
+worker_classes: Dict[str, Type["QueueProcessingWorker"]] = {}
+queues: Dict[str, Dict[str, Type["QueueProcessingWorker"]]] = {}

-AUTH_LDAP_REVERSE_EMAIL_SEARCH: Optional[LDAPSearch] = None
+AUTH_LDAP_REVERSE_EMAIL_SEARCH: Optional["LDAPSearch"] = None

Signed-off-by: Anders Kaseorg <anders@zulipchat.com>

zerver/lib/streams.py

@@ -86,8 +86,8 @@ def create_streams_if_needed(realm: Realm,
                              stream_dicts: List[Mapping[str, Any]]) -> Tuple[List[Stream], List[Stream]]:
     """Note that stream_dict["name"] is assumed to already be stripped of
     whitespace"""
-    added_streams = []  # type: List[Stream]
-    existing_streams = []  # type: List[Stream]
+    added_streams: List[Stream] = []
+    existing_streams: List[Stream] = []
     for stream_dict in stream_dicts:
         stream, created = create_stream_if_needed(
             realm,
@@ -361,7 +361,7 @@ def can_access_stream_history_by_id(user_profile: UserProfile, stream_id: int) -
 
 def filter_stream_authorization(user_profile: UserProfile,
                                 streams: Iterable[Stream]) -> Tuple[List[Stream], List[Stream]]:
-    streams_subscribed = set()  # type: Set[int]
+    streams_subscribed: Set[int] = set()
     recipient_ids = [stream.recipient_id for stream in streams]
     subs = Subscription.objects.filter(user_profile=user_profile,
                                        recipient_id__in=recipient_ids,
@@ -370,7 +370,7 @@ def filter_stream_authorization(user_profile: UserProfile,
     for sub in subs:
         streams_subscribed.add(sub.recipient.type_id)
 
-    unauthorized_streams = []  # type: List[Stream]
+    unauthorized_streams: List[Stream] = []
     for stream in streams:
         # The user is authorized for their own streams
         if stream.id in streams_subscribed:
@@ -411,8 +411,8 @@ def list_to_streams(streams_raw: Iterable[Mapping[str, Any]],
         assert stream_name == stream_name.strip()
         check_stream_name(stream_name)
 
-    existing_streams = []  # type: List[Stream]
-    missing_stream_dicts = []  # type: List[Mapping[str, Any]]
+    existing_streams: List[Stream] = []
+    missing_stream_dicts: List[Mapping[str, Any]] = []
     existing_stream_map = bulk_get_streams(user_profile.realm, stream_set)
 
     member_creating_announcement_only_stream = False
@@ -438,7 +438,7 @@ def list_to_streams(streams_raw: Iterable[Mapping[str, Any]],
     if len(missing_stream_dicts) == 0:
         # This is the happy path for callers who expected all of these
         # streams to exist already.
-        created_streams = []  # type: List[Stream]
+        created_streams: List[Stream] = []
     else:
         # autocreate=True path starts here
         if not user_profile.can_create_streams():