[QGIS-Developer] pyqgis getFeatures(<FilterExpression>) doesn't always fetch modified geometry

[Erik Polzin]

Hi all,

Noticed some strange behaviour in QGIS' Python API the other day.
I needed to get a subset of points from a memory layer of point features,
and had previously done so by calling getFeatures(), and then filtering
this iterable in Python. I thought I could speed it up by using a filter
expression directly to let c++ do the filtering instead, but was surprised
to see that now the geometry wasn't up to date with the memory layer's edit
buffer.

I've replicated the behaviour it in a small script here:

from qgis.core import QgsVectorLayer, QgsField, QgsGeometry, QgsPointXY,
QgsFeature
from PyQt5.QtCore import QVariant

layer = QgsVectorLayer("Point", "test", "memory")
pr = layer.dataProvider()
pr.addAttributes([QgsField("name", QVariant.String)])
layer.updateFields()

initialGeom = QgsGeometry.fromPointXY(QgsPointXY(0, 0))
f = QgsFeature()
f.setGeometry(initialGeom)
f.setAttributes(["Tom"])
added, (f,) = layer.dataProvider().addFeatures([f])

layer.startEditing()
editedGeom = QgsGeometry.fromPointXY(QgsPointXY(1, 1))
layer.changeGeometry(f.id(), editedGeom)
layer.changeAttributeValues(f.id(), {0: "Harry"})

for f in layer.getFeatures():
    print(f.id(), f.attributes(), f.geometry())

for f in layer.getFeatures("name = 'Harry'"):
    print(f.id(), f.attributes(), f.geometry())

# >>> Prints different results!

This only seems to happen with both calls to changeGeometry and
changeAttributeValues.
Is there some way of getting around this? Would it be classified as a bug
in the API?

Cheers,
Erik
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