Use __slots__ for tab.TabData

qutebrowser/browser/tab.py

@@ -74,27 +74,18 @@ class TabData:
     """A simple namespace with a fixed set of attributes.
 
     Attributes:
-        _initializing: Set when we're currently in __init__.
         keep_icon: Whether the (e.g. cloned) icon should not be cleared on page
                    load.
         inspector: The QWebInspector used for this webview.
         viewing_source: Set if we're currently showing a source view.
     """
 
+    __slots__ = ['keep_icon', 'viewing_source', 'inspector']
+
     def __init__(self):
-        self._initializing = True
         self.keep_icon = False
         self.viewing_source = False
         self.inspector = None
-        self._initializing = False
-
-    def __setattr__(self, attr, value):
-        if (attr == '_initializing' or
-                getattr(self, '_initializing', False) or
-                hasattr(self, attr)):
-            return super().__setattr__(attr, value)
-        msg = "Can't set unknown attribute {!r}".format(attr)
-        raise AttributeError(msg)
 
 
 class AbstractSearch(QObject):