Python: why is __dict__ attribute not in built-in class instances

Just to add to this:

You can get the equivalent of a read only __dict__ using this:

{s:getattr(x, s) for s in dir(x)}

EDIT: Please note that this may contain more entries than __dict__. To avert this, you may use this as a workaround:

{s:getattr(x, s) for s in dir(x) if not s.startswith("__")}

Instances of types defined in C don't have a __dict__ attribute by default.