will be returned ref(actually defines typereferencetypethat can be used for type-checking and subclasses proxy(object[callback]creates proxy using weak reference to object the returned proxy object is really wrapper around the original object that provides access to its attributes and methods as long as the original object existsmanipulation of the proxy object will transparently mimic the behavior of the underlying object on the other handif the original object has been destroyedoperations on the proxy will raise weakref referenceerror to indicate that the object no longer exists callback is callback function with the same meaning as for the ref(function the type of proxy object is either proxytype or callableproxytypedepending on whether or not the original object is callable getweakrefcount(objectreturns the number of weak references and proxies that refer to object getweakrefs(objectreturns list of all weak reference and proxy objects that refer to object weakkeydictionary([dict]creates dictionary in which the keys are referenced weakly when there are no more strong references to keythe corresponding entry in the dictionary is automatically removed if suppliedthe items in dict are initially added to the returned weakkeydictionary object because only certain types of objects can be weakly referencedthere are numerous restrictions on acceptable key values in particularbuilt-in strings cannot be used as weak keys howeverinstances of user-defined classes that define _hash_ (method can be used as keys an instance of weakkeydictionary has two methodsiterkeyrefs(and keyrefs()that return the weak key references weakvaluedictionary([dict]creates dictionary in which the values are referenced weakly when there are no more strong references to valuecorresponding entries in the dictionary will be discarded if suppliedthe entries in dict are added to the returned weakvaluedictionary an instance of weakvaluedictionary has two methodsitervaluerefs(and valuerefs()that return the weak value references proxytypes this is tuple (proxytypecallableproxytypethat can be used for testing if an object is one of the two kinds of proxy objects created by the proxy(function--for exampleisinstance(objectproxytypesf lib fl ff