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.. _advanced-weakref:
Atom and weak references
========================
.. include:: ../substitutions.sub
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:
.. code-block:: python
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.
.. code-block:: python
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.
.. code-block:: python
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
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