qgis - How to change the value of an attribute using QgsFeature in PyQGIS?

I would like to update one attribute of a feature. However, I don't know to update it using the feature object. I have to use data provider to update it.

layers = QgsMapLayerRegistry.instance().mapLayersByName('my_line') 

layer = layers[0]
dp = layer.dataProvider()
it = dp.getFeatures()

for i in range(0, dp.featureCount()):
  feat = it.next()
  attrs = { 2 : 30 }
  layer.dataProvider().changeAttributeValues({ feat.id() : attrs })

Can I change the value of an attribute using QgsFeature object?

Moreover, is it possible to loop using an iterator object?

Answer

Answering your two questions:

1. 
   

   You can change your feature values from the layer object, no need to access the dataProvider().

   
   


2. 
   

   Yes, you can use the iterator in a for loop.

   
   

Check the code below:

layers = QgsMapLayerRegistry.instance().mapLayersByName('my_line') 
layer = layers[0]
it = layer.getFeatures()

layer.startEditing()
for feat in it:
  layer.changeAttributeValue(feat.id(), 2, 30)


layer.commitChanges()

This updates the third (index 2) field value to 30 for all layer features.

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Note: As you pointed out, for some reason the QgsFeature object cannot update feature values, although the API says it can.