# Atom and weak references

Because atom objects are slotted by default and do not have an instance an instance dictionary, they do not support weak references by defaults.

Depending on the context in which you need weak references, you have two options:

- if you need weak references to interact with an external library (such as pyqt), you will need to enable the standard weakref mechanism.

- if you use weak references only internally and memory is a concern (Python standard weak references have a not so small overhead), you can use an alternative mechanism provided by atom.

## Enabling default weak references

In order to use the standard weak references of Python, you simply need to add the proper slot to your object as illustrated below:

    from atom.api import Atom

    MyWeakRefAtom(Atom):

        __slots__ = ('__weakref__',)

Note

Starting with atom 0.8.0 you can use the metaclass keyword argument enable_weakrefs to achieve the same result.

    from atom.api import Atom

    MyWeakRefAtom(Atom, enable_weakrefs=True):
        pass

## Using atom builtin weak references: `atomref`

To create a weak reference to atom object using the builtin mechanism, you simply have to create an instance of `atomref` using the object to reference as argument.

In order to access the object referenced by the `atomref`, you simply need to call it which will return the object. If the referenced object is not alive anymore, `atomref` will return None.

    import gc
    from atom.api import Atom, atomref

    class MyAtom(Atom):
        pass

    obj = MyAtom()
    ref = atomref(obj)

    assert obj is ref()

    del obj
    gc.collect()
    assert ref() is None