Dead weakrefs to a given object happen to be equal if they don't have a callback, but unequal if they do. However, they are always equal when alive: >>> class O: pass ... >>> o = O() >>> def cb(_): pass ... >>> q = weakref.ref(o) >>> r = weakref.ref(o) >>> s = weakref.ref(o, cb) >>> t = weakref.ref(o, cb) >>> q == r True >>> s == t True >>> del o >>> q() is None True >>> q == r True >>> s == t False This may be related to the following optimization (?): >>> q is r True >>> s is t False