问题
In Python weakref document( http://docs.python.org/library/weakref.html ), it says that
Several built-in types such as list and dict do not directly support weak references but can add support through subclassing
I think creating weakref for big dict could be useful in some real cases. I'm wondering what's the reason behind that implementation ?
回答1:
Most of the built-in types are not directly weak referenceable (e.g. str, int, float, list, dict, None), and there are a few that cannot even be made so by sub-classing (e.g. tuples in CPython).
Some details about the underlying implementation of weakrefs for several built-in types can be found in this March-2005 python-list post by Raymond Hettinger.
回答2:
My educated guess is that dicts and lists are used internally to implement weakrefs, so you would have an egg-chicken situation here.
来源：https://stackoverflow.com/questions/7711246/why-weakref-doesnt-support-built-in-types-in-python