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Selecting and updating attribute values using Python console in QGIS?

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2

I am working with Landusefc and Class columns (ref table).

What I want is: Selecting all water from "Class" and giving a value say '8' in the "Landusefc" column for these selected features.

Table looks like

I have tried the following code, it works till the selection part but doesn't seem to change the attribute value using the ChangeAttributeValue.

from qgis.core import *

import processing

layer=processing.getObject('test1')

query= ' "class" = 'Water' '

selection = layer.getFeatures(QgsFeatureRequest().setFilterExpression(query))

layer.setSelectedFeatures([k.id() for k in selection])



#using change Attribute to change the value of the selected feature



layer.startEditing()

for feat in selection:

     layer.changeAttributeValue(feat.id(), 5, 8)



layer.commitChanges()

qgis pyqgis select-by-attribute

share|improve this question

edited 17 hours ago

Kadir Şahbaz

4,63721531

asked 18 hours ago

ShellyShelly

212

add a comment | 

2

I am working with Landusefc and Class columns (ref table).

What I want is: Selecting all water from "Class" and giving a value say '8' in the "Landusefc" column for these selected features.

Table looks like

I have tried the following code, it works till the selection part but doesn't seem to change the attribute value using the ChangeAttributeValue.

from qgis.core import *

import processing

layer=processing.getObject('test1')

query= ' "class" = 'Water' '

selection = layer.getFeatures(QgsFeatureRequest().setFilterExpression(query))

layer.setSelectedFeatures([k.id() for k in selection])



#using change Attribute to change the value of the selected feature



layer.startEditing()

for feat in selection:

     layer.changeAttributeValue(feat.id(), 5, 8)



layer.commitChanges()

qgis pyqgis select-by-attribute

share|improve this question

edited 17 hours ago

Kadir Şahbaz

4,63721531

asked 18 hours ago

ShellyShelly

212

add a comment | 

I am working with Landusefc and Class columns (ref table).

What I want is: Selecting all water from "Class" and giving a value say '8' in the "Landusefc" column for these selected features.

Table looks like

I have tried the following code, it works till the selection part but doesn't seem to change the attribute value using the ChangeAttributeValue.

from qgis.core import *

import processing

layer=processing.getObject('test1')

query= ' "class" = 'Water' '

selection = layer.getFeatures(QgsFeatureRequest().setFilterExpression(query))

layer.setSelectedFeatures([k.id() for k in selection])



#using change Attribute to change the value of the selected feature



layer.startEditing()

for feat in selection:

     layer.changeAttributeValue(feat.id(), 5, 8)



layer.commitChanges()

qgis pyqgis select-by-attribute

share|improve this question

edited 17 hours ago

Kadir Şahbaz

4,63721531

asked 18 hours ago

ShellyShelly

212

from qgis.core import *

import processing

layer=processing.getObject('test1')

query= ' "class" = 'Water' '

selection = layer.getFeatures(QgsFeatureRequest().setFilterExpression(query))

layer.setSelectedFeatures([k.id() for k in selection])



#using change Attribute to change the value of the selected feature



layer.startEditing()

for feat in selection:

     layer.changeAttributeValue(feat.id(), 5, 8)



layer.commitChanges()

share|improve this question

edited 17 hours ago

Kadir Şahbaz

4,63721531

asked 18 hours ago

ShellyShelly

212

share|improve this question

edited 17 hours ago

Kadir Şahbaz

4,63721531

asked 18 hours ago

ShellyShelly

212

edited 17 hours ago

Kadir Şahbaz

4,63721531

edited 17 hours ago

Kadir Şahbaz

4,63721531

asked 18 hours ago

ShellyShelly

212

asked 18 hours ago

ShellyShelly

212

1 Answer
1

active

oldest

votes

2

SOLUTION 1:

You have to remove layer.setSelectedFeatures([k.id() for k in selection]).

Because selection = layer.getFeatures(QgsFeatureRequest().setFilterExpression(query)) line gives you a QgsFeatureIterator, that's an iterator. When you use that iterator once, you reach the end of the iterator. Then, if you use it again, you get nothing.

In your case, when you use selection variable (it's an iterator now) in [k.id() for k in selection], you reach the end. If you use selection in for loop, since you are at the end of the iterator, you don't have any feature now. If you want to be certain, you can add a print("Foo") line to for loop.

SOLUTION 2:

Change for feat in selection: into for feat in layer.selectedFeatures():. This solution works only on QGIS 2.x.

share|improve this answer

edited 15 hours ago

answered 17 hours ago

Kadir ŞahbazKadir Şahbaz

4,63721531

add a comment | 

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2

SOLUTION 1:

You have to remove layer.setSelectedFeatures([k.id() for k in selection]).

Because selection = layer.getFeatures(QgsFeatureRequest().setFilterExpression(query)) line gives you a QgsFeatureIterator, that's an iterator. When you use that iterator once, you reach the end of the iterator. Then, if you use it again, you get nothing.

In your case, when you use selection variable (it's an iterator now) in [k.id() for k in selection], you reach the end. If you use selection in for loop, since you are at the end of the iterator, you don't have any feature now. If you want to be certain, you can add a print("Foo") line to for loop.

SOLUTION 2:

Change for feat in selection: into for feat in layer.selectedFeatures():. This solution works only on QGIS 2.x.

share|improve this answer

edited 15 hours ago

answered 17 hours ago

Kadir ŞahbazKadir Şahbaz

4,63721531

add a comment | 

2

SOLUTION 1:

You have to remove layer.setSelectedFeatures([k.id() for k in selection]).

Because selection = layer.getFeatures(QgsFeatureRequest().setFilterExpression(query)) line gives you a QgsFeatureIterator, that's an iterator. When you use that iterator once, you reach the end of the iterator. Then, if you use it again, you get nothing.

In your case, when you use selection variable (it's an iterator now) in [k.id() for k in selection], you reach the end. If you use selection in for loop, since you are at the end of the iterator, you don't have any feature now. If you want to be certain, you can add a print("Foo") line to for loop.

SOLUTION 2:

Change for feat in selection: into for feat in layer.selectedFeatures():. This solution works only on QGIS 2.x.

share|improve this answer

edited 15 hours ago

answered 17 hours ago

Kadir ŞahbazKadir Şahbaz

4,63721531

add a comment | 

SOLUTION 1:

You have to remove layer.setSelectedFeatures([k.id() for k in selection]).

Because selection = layer.getFeatures(QgsFeatureRequest().setFilterExpression(query)) line gives you a QgsFeatureIterator, that's an iterator. When you use that iterator once, you reach the end of the iterator. Then, if you use it again, you get nothing.

In your case, when you use selection variable (it's an iterator now) in [k.id() for k in selection], you reach the end. If you use selection in for loop, since you are at the end of the iterator, you don't have any feature now. If you want to be certain, you can add a print("Foo") line to for loop.

SOLUTION 2:

Change for feat in selection: into for feat in layer.selectedFeatures():. This solution works only on QGIS 2.x.

share|improve this answer

edited 15 hours ago

answered 17 hours ago

Kadir ŞahbazKadir Şahbaz

4,63721531

share|improve this answer

edited 15 hours ago

answered 17 hours ago

Kadir ŞahbazKadir Şahbaz

4,63721531

answered 17 hours ago

Kadir ŞahbazKadir Şahbaz

4,63721531

answered 17 hours ago

Kadir ŞahbazKadir Şahbaz

4,63721531