[Python] How to get stretch factor for QSpacerItems

When you addStretch() or insertStretch() to a QBoxLayout, a QSpacerItem is added/inserted to the layout and you can set the stretch factor while doing so.

Now I would like to retrieve that stretch factor from the SpacerItem but I can't find how to do so.
item.sizePolicy().verticalStretch() always returns 0, as can be demonstrated with this example:

from PyQt6.QtWidgets import QApplication, QWidget, QVBoxLayout, QPushButton, QSpacerItem


class Window(QWidget):
def __init__(self):
super().__init__()
self.setGeometry(700, 500, 100, 200)
self.layout = QVBoxLayout(self)

for i in range(3):
but = QPushButton(f'Push {i}')
self.layout.addWidget(but)
if i == 0:
but.clicked.connect(self.click)

self.layout.insertStretch(1, 2)
self.layout.insertStretch(3, 3)

def click(self):
for i in (1, 3):
stretch = self.layout.itemAt(i)
assert isinstance(stretch, QSpacerItem)
pol = stretch.sizePolicy()
print(pol.verticalStretch())


app = QApplication([])
window = Window()
window.show()
app.exec()


So where is the stretch factor stored? and is this info accessible somehow or would I have to keep a separate reference to keep the stretch info available?

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