Rotating features with multiple geometries in one layer using PyQGIS

Question

I have a layer containing several small square geometries in QGIS. I want to tilt these ones by one to the same angle. So I wrote the following Python code for that, but it does not work properly. Could you please give me some suggestions for improvement?

#import processing

layer_name = "my_layer"

layer = QgsProject.instance().mapLayersByName(layer_name)[0]

features = layer.getFeatures()

for feature in features:
  geometry = feature.geometry()
  center = geometry.centroid().asPoint()
  rotated_geometry = geometry.rotate(33, center)
  feature.setGeometry(rotated_geometry)
  layer.updateFeature(feature)

layer.updateExtents()

Answer 1

There are several things that I would improve:

• do not forget to start/startEditing, end/endEditCommand(), and commit/commitChanges() editings

• use the setGeometry() method properly, otherwise the result of it will be just GeometryOperationResult.Success

• make your code homogeneous

   layer = QgsProject.instance().mapLayersByName("polygon")[0]
   ...
       geometry.rotate(33, center)
  

  or

   layer_name = "polygon"
   angle = 33
  
   layer = QgsProject.instance().mapLayersByName(layer_name)[0]
   ...
       geometry.rotate(angle, center)
  

• use for feature in layer.getFeatures() in one line

• import only classes that are deployed, no need for the import processing

• the hasGeometry() method of the QgsFeature class can be useful

In the end, your code may look as follows:

from qgis.core import QgsProject

layer = QgsProject.instance().mapLayersByName("my_layer")[0]

layer.startEditing()

for feature in layer.getFeatures():
    while feature.hasGeometry():
        geometry = feature.geometry()
        center = geometry.centroid().asPoint()
        geometry.rotate(33, center)
        feature.setGeometry(geometry)
        layer.updateFeature(feature)
        break
    
layer.endEditCommand()
layer.commitChanges()

Note: Remember that applied changes can not be undone.

Another approach can be found in the references.

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References:

• Rotating features in memory layer using PyQGIS