zerver/lib: Use python 3 syntax for typing.

Extracted from a larger commit by tabbott because these changes will
not create significant merge conflicts.

zerver/lib/exceptions.py

@@ -6,24 +6,20 @@ from django.core.exceptions import PermissionDenied
 class AbstractEnum(Enum):
     '''An enumeration whose members are used strictly for their names.'''
 
-    def __new__(cls):
-        # type: (Type[AbstractEnum]) -> AbstractEnum
+    def __new__(cls: Type['AbstractEnum']) -> 'AbstractEnum':
         obj = object.__new__(cls)
         obj._value_ = len(cls.__members__) + 1
         return obj
 
     # Override all the `Enum` methods that use `_value_`.
 
-    def __repr__(self):
-        # type: () -> str
+    def __repr__(self) -> str:
         return str(self)
 
-    def value(self):
-        # type: () -> None
+    def value(self) -> None:
         assert False
 
-    def __reduce_ex__(self, proto):
-        # type: (int) -> None
+    def __reduce_ex__(self, proto: int) -> None:
         assert False
 
 class ErrorCode(AbstractEnum):
@@ -69,13 +65,11 @@ class JsonableError(Exception):
              code = ErrorCode.NO_SUCH_WIDGET
              data_fields = ['widget_name']
 
-             def __init__(self, widget_name):
-                 # type: (str) -> None
+             def __init__(self, widget_name: str) -> None:
                  self.widget_name = widget_name  # type: str
 
              @staticmethod
-             def msg_format():
-                 # type: () -> str
+             def msg_format() -> str:
                  return _("No such widget: {widget_name}")
 
          raise NoSuchWidgetError(widget_name)
@@ -96,8 +90,7 @@ class JsonableError(Exception):
     # like 403 or 404.
     http_status_code = 400  # type: int
 
-    def __init__(self, msg, code=None):
-        # type: (Text, Optional[ErrorCode]) -> None
+    def __init__(self, msg: Text, code: Optional[ErrorCode]=None) -> None:
         if code is not None:
             self.code = code
 
@@ -105,8 +98,7 @@ class JsonableError(Exception):
         self._msg = msg  # type: Text
 
     @staticmethod
-    def msg_format():
-        # type: () -> Text
+    def msg_format() -> Text:
         '''Override in subclasses.  Gets the items in `data_fields` as format args.
 
         This should return (a translation of) a string literal.
@@ -124,29 +116,24 @@ class JsonableError(Exception):
     #
 
     @property
-    def msg(self):
-        # type: () -> Text
+    def msg(self) -> Text:
         format_data = dict(((f, getattr(self, f)) for f in self.data_fields),
                            _msg=getattr(self, '_msg', None))
         return self.msg_format().format(**format_data)
 
     @property
-    def data(self):
-        # type: () -> Dict[str, Any]
+    def data(self) -> Dict[str, Any]:
         return dict(((f, getattr(self, f)) for f in self.data_fields),
                     code=self.code.name)
 
-    def to_json(self):
-        # type: () -> Dict[str, Any]
+    def to_json(self) -> Dict[str, Any]:
         d = {'result': 'error', 'msg': self.msg}
         d.update(self.data)
         return d
 
-    def __str__(self):
-        # type: () -> str
+    def __str__(self) -> str:
         return self.msg
 
 class RateLimited(PermissionDenied):
-    def __init__(self, msg=""):
-        # type: (str) -> None
+    def __init__(self, msg: str="") -> None:
         super().__init__(msg)