lambda python reference count

reference_count.py

from pyqtgraph.Qt import QtWidgets
import weakref
import gc

class MyButton(QtWidgets.QPushButton):
    def __init__(self, *args, **kwds):
        super().__init__(*args, **kwds)
        self.clicked.connect(lambda : self.hello())
        # self.clicked.connect(lambda: QtWidgets.QApplication.instance().exit())
        # self.clicked.connect(self.hello)

    def hello(self):
        QtWidgets.QApplication.instance().exit()

app = QtWidgets.QApplication([])
button = MyButton("Hello")
button.show()
app.exec() if hasattr(app, 'exec') else app.exec_()

ref = weakref.ref(button)
del button
print(ref())
gc.collect()
print(ref())