Replace _event_dict_property with DictProperty

this amounts to the same thing, but replaces `_event_dict` with `_dict`, and
removes some of the function layers generated by `property`.

2 files changed, 80 insertions, 66 deletions

diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index a842661a90..512254f65d 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -37,6 +37,65 @@ from synapse.util.frozenutils import freeze
 USE_FROZEN_DICTS = strtobool(os.environ.get("SYNAPSE_USE_FROZEN_DICTS", "0"))
 
 
+class DictProperty:
+    """An object property which delegates to the `_dict` within its parent object."""
+
+    __slots__ = ["key"]
+
+    def __init__(self, key: str):
+        self.key = key
+
+    def __get__(self, instance, owner=None):
+        # if the property is accessed as a class property rather than an instance
+        # property, return the property itself rather than the value
+        if instance is None:
+            return self
+        try:
+            return instance._dict[self.key]
+        except KeyError as e1:
+            # We want this to look like a regular attribute error (mostly so that
+            # hasattr() works correctly), so we convert the KeyError into an
+            # AttributeError.
+            #
+            # To exclude the KeyError from the traceback, we explicitly
+            # 'raise from e1.__context__' (which is better than 'raise from None',
+            # becuase that would omit any *earlier* exceptions).
+            #
+            raise AttributeError(
+                "'%s' has no '%s' property" % (type(instance), self.key)
+            ) from e1.__context__
+
+    def __set__(self, instance, v):
+        instance._dict[self.key] = v
+
+    def __delete__(self, instance):
+        try:
+            del instance._dict[self.key]
+        except KeyError as e1:
+            raise AttributeError(
+                "'%s' has no '%s' property" % (type(instance), self.key)
+            ) from e1.__context__
+
+
+class DefaultDictProperty(DictProperty):
+    """An extension of DictProperty which provides a default if the property is
+    not present in the parent's _dict.
+
+    Note that this means that hasattr() on the property always returns True.
+    """
+
+    __slots__ = ["default"]
+
+    def __init__(self, key, default):
+        super().__init__(key)
+        self.default = default
+
+    def __get__(self, instance, owner=None):
+        if instance is None:
+            return self
+        return instance._dict.get(self.key, self.default)
+
+
 class _EventInternalMetadata(object):
     def __init__(self, internal_metadata_dict):
         self.__dict__ = dict(internal_metadata_dict)
@@ -117,51 +176,6 @@ class _EventInternalMetadata(object):
         return getattr(self, "redacted", False)
 
 
-_SENTINEL = object()
-
-
-def _event_dict_property(key, default=_SENTINEL):
-    """Creates a new property for the given key that delegates access to
-    `self._event_dict`.
-
-    The default is used if the key is missing from the `_event_dict`, if given,
-    otherwise an AttributeError will be raised.
-
-    Note: If a default is given then `hasattr` will always return true.
-    """
-
-    # We want to be able to use hasattr with the event dict properties.
-    # However, (on python3) hasattr expects AttributeError to be raised. Hence,
-    # we need to transform the KeyError into an AttributeError
-
-    def getter_raises(self):
-        try:
-            return self._event_dict[key]
-        except KeyError:
-            raise AttributeError(key)
-
-    def getter_default(self):
-        return self._event_dict.get(key, default)
-
-    def setter(self, v):
-        try:
-            self._event_dict[key] = v
-        except KeyError:
-            raise AttributeError(key)
-
-    def delete(self):
-        try:
-            del self._event_dict[key]
-        except KeyError:
-            raise AttributeError(key)
-
-    if default is _SENTINEL:
-        # No default given, so use the getter that raises
-        return property(getter_raises, setter, delete)
-    else:
-        return property(getter_default, setter, delete)
-
-
 class EventBase(object):
     def __init__(
         self,
@@ -175,23 +189,23 @@ class EventBase(object):
         self.unsigned = unsigned
         self.rejected_reason = rejected_reason
 
-        self._event_dict = event_dict
+        self._dict = event_dict
 
         self.internal_metadata = _EventInternalMetadata(internal_metadata_dict)
 
-    auth_events = _event_dict_property("auth_events")
-    depth = _event_dict_property("depth")
-    content = _event_dict_property("content")
-    hashes = _event_dict_property("hashes")
-    origin = _event_dict_property("origin")
-    origin_server_ts = _event_dict_property("origin_server_ts")
-    prev_events = _event_dict_property("prev_events")
-    redacts = _event_dict_property("redacts", None)
-    room_id = _event_dict_property("room_id")
-    sender = _event_dict_property("sender")
-    state_key = _event_dict_property("state_key")
-    type = _event_dict_property("type")
-    user_id = _event_dict_property("sender")
+    auth_events = DictProperty("auth_events")
+    depth = DictProperty("depth")
+    content = DictProperty("content")
+    hashes = DictProperty("hashes")
+    origin = DictProperty("origin")
+    origin_server_ts = DictProperty("origin_server_ts")
+    prev_events = DictProperty("prev_events")
+    redacts = DefaultDictProperty("redacts", None)
+    room_id = DictProperty("room_id")
+    sender = DictProperty("sender")
+    state_key = DictProperty("state_key")
+    type = DictProperty("type")
+    user_id = DictProperty("sender")
 
     @property
     def event_id(self) -> str:
@@ -205,13 +219,13 @@ class EventBase(object):
         return hasattr(self, "state_key") and self.state_key is not None
 
     def get_dict(self) -> JsonDict:
-        d = dict(self._event_dict)
+        d = dict(self._dict)
         d.update({"signatures": self.signatures, "unsigned": dict(self.unsigned)})
 
         return d
 
     def get(self, key, default=None):
-        return self._event_dict.get(key, default)
+        return self._dict.get(key, default)
 
     def get_internal_metadata_dict(self):
         return self.internal_metadata.get_dict()
@@ -233,16 +247,16 @@ class EventBase(object):
         raise AttributeError("Unrecognized attribute %s" % (instance,))
 
     def __getitem__(self, field):
-        return self._event_dict[field]
+        return self._dict[field]
 
     def __contains__(self, field):
-        return field in self._event_dict
+        return field in self._dict
 
     def items(self):
-        return list(self._event_dict.items())
+        return list(self._dict.items())
 
     def keys(self):
-        return six.iterkeys(self._event_dict)
+        return six.iterkeys(self._dict)
 
     def prev_event_ids(self):
         """Returns the list of prev event IDs. The order matches the order
diff --git a/tests/storage/test_redaction.py b/tests/storage/test_redaction.py
index b9ee6ec1ec..db3667dc43 100644
--- a/tests/storage/test_redaction.py
+++ b/tests/storage/test_redaction.py
@@ -240,7 +240,7 @@ class RedactionTestCase(unittest.HomeserverTestCase):
                 built_event = yield self._base_builder.build(prev_event_ids)
 
                 built_event._event_id = self._event_id
-                built_event._event_dict["event_id"] = self._event_id
+                built_event._dict["event_id"] = self._event_id
                 assert built_event.event_id == self._event_id
 
                 return built_event