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(input ,"line","ogr")
temp = QgsVectorLayer("LineString?crs=epsg:4326", "result", "memory")
temp_data = temp.dataProvider()
temp.startEditing()
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)

Answer 1

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.

enter image description here

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:

enter image description here

• Joseph: I very much appreciate your answer, much shorter alternative to what I had. Thank you!

Answer 2

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

feat.setAttributes(elem.attributes())