Copying weakrefs
I am working with an object, Context, that maintains an identity map by using the weakref.WeakValueDictionary. I would like to clone this Context object (and objects that may have a Context object) using copy.deepcopy(). When I try to do this, the deep copy operation recurses down to the WeakValueDictionary, down to the KeyedRef subclass of ref, and then fails. It seems that copy.copy() and copy.deepcopy() operations on weakrefs just won't work. The failure can be replicated with this (much simpler) scenario: >>> import weakref, copy >>> class Test(object): pass >>> t = Test() >>> wr = weakref.ref(t) >>> wr_new = copy.copy(wr) # Fails, not enough args to __new__ Anybody out there have some insight into this? Thanks Rick -- http://mail.python.org/mailman/listinfo/python-list
Re: Copying weakrefs
On Feb 14, 12:31 pm, Rick Harris <[EMAIL PROTECTED]> wrote: > I am working with an object, Context, that maintains an identity map > by using the weakref.WeakValueDictionary. I would like to clone this > Context object (and objects that may have a Context object) using > copy.deepcopy(). When I try to do this, the deep copy operation > recurses down to the WeakValueDictionary, down to the KeyedRef > subclass of ref, and then fails. It seems that copy.copy() and > copy.deepcopy() operations on weakrefs just won't work. > > The failure can be replicated with this (much simpler) scenario: > > >>> import weakref, copy > >>> class Test(object): pass > >>> t = Test() > >>> wr = weakref.ref(t) > >>> wr_new = copy.copy(wr) # Fails, not enough args to __new__ > > Anybody out there have some insight into this? > > Thanks > Rick Update: I was able to monkey-patch the copy module's dispatch tables to (seemingly) fix this. The code is: >>> copy._copy_dispatch[weakref.ref] = copy._copy_immutable >>> copy._deepcopy_dispatch[weakref.KeyedRef] = copy._deepcopy_atomic Could somebody more familiar with Python internals look into whether this patch is a) correct and b) whether this should be added to copy module? Thanks, Rick -- http://mail.python.org/mailman/listinfo/python-list
Re: Copying weakrefs
On Feb 14, 12:31 pm, Rick Harris <[EMAIL PROTECTED]> wrote: > I am working with an object, Context, that maintains an identity map > by using the weakref.WeakValueDictionary. I would like to clone this > Context object (and objects that may have a Context object) using > copy.deepcopy(). When I try to do this, the deep copy operation > recurses down to the WeakValueDictionary, down to the KeyedRef > subclass of ref, and then fails. It seems that copy.copy() and > copy.deepcopy() operations on weakrefs just won't work. > > The failure can be replicated with this (much simpler) scenario: > > >>> import weakref, copy > >>> class Test(object): pass > >>> t = Test() > >>> wr = weakref.ref(t) > >>> wr_new = copy.copy(wr) # Fails, not enough args to __new__ > > Anybody out there have some insight into this? > > Thanks > Rick Update: Adding the following monkey-patch seems to fix the problem: >>> copy._copy_dispatch[weakref.ref] = copy._copy_immutable >>> copy._deepcopy_dispatch[weakref.KeyedRef] = copy._deepcopy_atomic Perhaps the copy module should be patched with something along these lines. Thanks, Rick -- http://mail.python.org/mailman/listinfo/python-list
