Carry over attributes from a point layer to a new buffer layer using Python in QGIS

Question

Using the code outlined in the question: How to create square buffers around points in QGIS with Python? I created a layer of square buffers from coordinate points, however I was unable to carry over all of the point attributes to the new layer.

We have the following columns in our point attributes:

BigCellID (integer),
BigCellTyp (integer),
x,
y

The following code carried over the x and y columns perfectly:

layer = iface.activeLayer()

feats = [ feat for feat in layer.getFeatures() ]

epsg = layer.crs().postgisSrid()

uri = "Polygon?crs=epsg:" + str(epsg) + "&field=id:integer&field=x:real&field=y:real&field=point_id:integer""&index=yes"

mem_layer = QgsVectorLayer(uri,
                           'square_buffer',
                           'memory')

prov = mem_layer.dataProvider()

for i, feat in enumerate(feats):
    point = feat.geometry().asPoint()
    new_feat = QgsFeature()
    new_feat.setAttributes([i, point[0], point[1], feat.id()])
    tmp_feat = feat.geometry().buffer(1000, -1).boundingBox().asWktPolygon()
    new_feat.setGeometry(QgsGeometry.fromWkt(tmp_feat))
    prov.addFeatures([new_feat])

QgsMapLayerRegistry.instance().addMapLayer(mem_layer)

However to get it to also carry over the other two columns I made the following modification to one line:

uri = "Polygon?crs=epsg:" + str(epsg) + "&field=id:integer&field=x:real&field=y:real&field=BigCelID:integer&field=BigCellTyp:integer""&index=yes"

instead of:

uri = "Polygon?crs=epsg:" + str(epsg) + "&field=id:integer&field=x:real&field=y:real&field=point_id:integer""&index=yes"

This modification did not affect the x and y columns being carried over, and did create new columns; but the column BigCellID was filled with sequentially increasing numbers from 0, while BigCellTyp was filled with 'Null'. These are not the original values.

I would like to know how I can modify this code to ensure the contents of my two columns BigCellID and BigCellTyp are carried over to the new buffer layer?

Answer 1

If you did this modification:

uri = "Polygon?crs=epsg:" + str(epsg) + "&field=id:integer&field=x:real&field=y:real&field=BigCelID:integer&field=BigCellTyp:integer""&index=yes"

you need this one:

.
.
.
for i, feat in enumerate(feats):
    .
    .
    .
    new_feat.setAttributes([i, point[0], point[1], BigCellID[i], BigCellTyp[i]])
    .
    .
    .

to fill all fields with values that you are expected. Of course, before the loop, you need to have BigCellID and BigCellTyp defined as a list of values with the same dimension of features number.

Editing Note:

As you said: "We have the following columns in our point attributes:

BigCellID (integer), BigCellTyp (integer)..."

so, next code should work well:

layer = iface.activeLayer()

feats = [ feat for feat in layer.getFeatures() ]

n = len(feats)

BigCellID = [ feats[i].attribute('BigCellID') for i in range(n) ]
BigCellTyp = [ feats[i].attribute('BigCellTyp') for i in range(n) ]

epsg = layer.crs().postgisSrid()

uri = "Polygon?crs=epsg:" + str(epsg) + "&field=id:integer&field=x:real&field=y:real&field=BigCelID:integer&field=BigCellTyp:integer""&index=yes" 
mem_layer = QgsVectorLayer(uri,
                           'square_buffer',
                           'memory')

prov = mem_layer.dataProvider()

for i, feat in enumerate(feats):
    point = feat.geometry().asPoint()
    new_feat = QgsFeature()
    new_feat.setAttributes([i, point[0], point[1], BigCellID[i], BigCellTyp[i]])
    tmp_feat = feat.geometry().buffer(1000, -1).boundingBox().asWktPolygon()
    new_feat.setGeometry(QgsGeometry.fromWkt(tmp_feat))
    prov.addFeatures([new_feat])

QgsMapLayerRegistry.instance().addMapLayer(mem_layer)

I tried it out with my own point layer (where I defined 'BigCellID' and 'BigCellTyp' fields with arbitrary values) and it works fine.