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The destroyed() signal can be trapped for a QObject, but I would like to simply test if the Python object still references a valid C++ Qt object. Is there a method for doing so directly?
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QObject is the heart of the Qt Object Model. The central feature in this model is a very powerful mechanism for seamless object communication called signals and slots. You can connect a signal to a slot with connect() and destroy the connection with disconnect().
To connect the signal to the slot, we use QObject::connect(). There are several ways to connect signal and slots. The first is to use function pointers: connect(sender, &QObject::destroyed, this, &MyObject::objectDestroyed); There are several advantages to using QObject::connect() with function pointers.
Is PyQt thread safe? Remarks# While some parts of the Qt framework are thread safe, much of it is not. The Qt C++ documentation provides a good overview of which classes are reentrant (can be used to instantiate objects in multiple threads).
If you import the sip module you can call its .isdeleted function.
import sip
from PyQt4.QtCore import QObject
q = QObject()
sip.isdeleted(q)
False
sip.delete(q)
q
<PyQt4.QtCore.QObject object at 0x017CCA98>
q.isdeleted(q)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RuntimeError: underlying C/C++ object has been deleted
You can use the WeakRef class in the Python standard library. It would look something like:
import weakref
q = QObject()
w = weakref.ref(q)
if w() is not None: # Remember the parentheses!
print('The QObject is still alive.')
else:
print('Looks like the QObject died.')
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