Go through QGIS Python for loop through features in reverse order?

Question

I am trying to go through a for loop in QGIS's Python module in reverse order for my features.

from qgis.utils import iface
from PyQt4.QtCore import *
layers = iface.legendInterface().layers()
for layer in layers:
    name = layer.name()
    myLayer = QgsMapLayerRegistry.instance().mapLayersByName( name )[0]
    if name.startswith('Test'):
        for f in layer.getFeatures():

I would like to be able to go through that second for loop in reverse order. I know python has the reversed() function but that is only for lists. I can't seem to use it for layer.getFeatures().

Is there a way to do this?

Perhaps you could do something like "features = sorted(layer.getFeatures(), key=get_name)" as shown over here by walkermatt: https://gis.stackexchange.com/questions/138769/is-it-possible-to-sort-the-features-by-an-attribute-programmatically — cm1, May 31 '18 at 20:43
This will work for what I need! Thanks for pointing this out — efrank, May 31 '18 at 22:03

score 2 · Accepted Answer · answered Jun 01 '18 at 01:01

getFeatures() by itself would return the features in an unpredictable order, so taking the reverse order is also unpredictable.

You can specify a QgsFeatureRequest containing an order by clause

from qgis.utils import iface
from PyQt4.QtCore import *
layers = iface.legendInterface().layers()
for layer in layers:
    name = layer.name()
    myLayer = QgsMapLayerRegistry.instance().mapLayersByName( name )[0]
    if name.startswith('Test'):
        #Specify the Order By clause. False means Descending
        for f in layer.getFeatures(QgsFeatureRequest().addOrderBy('IDfield',False)):

Go through QGIS Python for loop through features in reverse order?

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