Creating memory layer and populate fields using PyQGIS

Question

Seems like a basic operation using PyQGIS but can't see what I am missing. I want to create a memory layer with the exact same features and attributes from a shapefile. I have looked several posts such as:

Copying attributes from point layer to memory linestring layer PYQGIS)
[URL IS BROKEN] PyQGIS manually copy all features with attributes from a layer into a memory layer

The following script creates a memory layer, gets the correct fields and correct number of features but it doesn't populate the fields with data:

input = "C:/Users/Me/Desktop//example.shp"
layer = QgsVectorLayer(example,"line","ogr")
temp = QgsVectorLayer("LineString?crs=epsg:4326", "result", "memory")
temp_data = temp.dataProvider()
temp.startEditing()
layer_fields = layer.dataProvider().fields().toList()
attr = layer.dataProvider().fields().toList()
temp_data.addAttributes(attr)
temp.updateFields()
feat = QgsFeature()
for elem in layer.getFeatures():
    feat.setGeometry(elem.geometry())
    feat.setAttributes(attr)
    temp.addFeatures([feat])
    temp.updateExtents()
temp.commitChanges()
QgsMapLayerRegistry.instance().addMapLayer(temp)

score 8 · Answer 1 · edited Jun 22 '22 at 07:00

I modified your code to consider a polygon vector layer. However, if you get the features of the original layer, you only need a little portion of your original code for working adequately (without any editing session if you use the QgsDataProvider class).

This is my code:

input = "/home/zeito/pyqgis_data/polygon8.shp"
layer = QgsVectorLayer(input,"polygon","ogr")
feats = [ feat for feat in layer.getFeatures() ]
temp = QgsVectorLayer("Polygon?crs=epsg:32612", "result", "memory")
QgsProject.instance().addMapLayer(temp)
temp_data = temp.dataProvider()
attr = layer.dataProvider().fields().toList()
temp_data.addAttributes(attr)
temp.updateFields()
temp_data.addFeatures(feats)

When above code was running at the Python Console (Ctrl+Alt+P) of QGIS, fields of original layer were correctly copied at the memory layer named "result"; as can be observed at the next image. It worked for me.

On the other hand, your approach of set attributes to a list of fields instead a list of values is correct because if I comment these code lines:

attr = layer.dataProvider().fields().toList()
temp_data.addAttributes(attr)

it doesn't populate the fields with data; as it also observed at the next image:

I very much appreciate your answer, much shorter alternative to what I had. Thank you! — Joseph, Dec 16 '15 at 10:13

score 4 · Accepted Answer · answered Dec 15 '15 at 17:26

4

Hmm, you set attributes to a list of fields instead a list of values. Try this:

feat.setAttributes(elem.attributes())

answered Dec 15 '15 at 17:26

Detlev

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Creating memory layer and populate fields using PyQGIS

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