expired()

Checks if the target object of a dbzero.weak_proxy has been garbage-collected.

This method is the counterpart to dbzero.weak_proxy(). After creating a weak reference to an object, you can use expired() to determine if the original object still exists in the store or if it has been removed.

Parameters

• proxy_object (dbzero.proxy): The weak proxy object, returned from dbzero.weak_proxy(), whose target you want to check.

Returns

• bool: Returns True if the object referenced by the proxy no longer exists. Returns False if the object is still present in the store.

Example

Here’s a typical lifecycle: create an object, create a weak proxy to it, delete the original object's strong references, and then check the proxy's status.

# Create an object that will be our target
original_obj = MyClass(value=123)
 
# Create another object that holds a weak proxy to the first one
wrapper_obj = OtherClass(ref=db0.weak_proxy(original_obj))
 
# The weak proxy is not expired yet, as original_obj still exists
assert not db0.expired(wrapper_obj.ref)
 
# Now, delete the only strong reference to the original object
del original_obj
db0.commit() # This will garbage-collect original_obj
 
# The proxy is now expired because its target is gone
assert db0.expired(wrapper_obj.ref) is True

# ... continuing from the example above ...
 
# Tag another object using the now-expired proxy
some_other_obj = AnotherClass()
db0.tags(some_other_obj).add(db0.as_tag(wrapper_obj.ref))
db0.commit()
 
# We can still find the tagged object using the expired proxy as a lookup key
found_objs = list(db0.find(db0.as_tag(wrapper_obj.ref)))
assert found_objs == [some_other_obj]