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/test_runner.py

@@ -80,7 +80,7 @@ def get_test_method(test: TestCase) -> Callable[[], None]:
     return getattr(test, test._testMethodName)
 
 # Each tuple is delay, test_name, slowness_reason
-TEST_TIMINGS = []  # type: List[Tuple[float, str, str]]
+TEST_TIMINGS: List[Tuple[float, str, str]] = []
 
 
 def report_slow_tests() -> None:
@@ -154,7 +154,7 @@ class TextTestResult(runner.TextTestResult):
 
     def __init__(self, *args: Any, **kwargs: Any) -> None:
         super().__init__(*args, **kwargs)
-        self.failed_tests = []  # type: List[str]
+        self.failed_tests: List[str] = []
 
     def addInfo(self, test: TestCase, msg: str) -> None:
         self.stream.write(msg)  # type: ignore[attr-defined] # https://github.com/python/typeshed/issues/3139
@@ -416,10 +416,10 @@ class Runner(DiscoverRunner):
 
         # `templates_rendered` holds templates which were rendered
         # in proper logical tests.
-        self.templates_rendered = set()  # type: Set[str]
+        self.templates_rendered: Set[str] = set()
         # `shallow_tested_templates` holds templates which were rendered
         # in `zerver.tests.test_templates`.
-        self.shallow_tested_templates = set()  # type: Set[str]
+        self.shallow_tested_templates: Set[str] = set()
         template_rendered.connect(self.on_template_rendered)
 
     def get_resultclass(self) -> Type[TestResult]: