After running processins in a loop, I try to export results on a single shapefile. I've created a vector layer called "regroupee", I merge results with it, and I overwrite "regroupee" with the result.

As Kadir Şahbaz said in this post on the option 8, run() method with memory output make a dictionnary, with an instance of a layer (QgsVectorLayer).

The loop works, but when I try to export the final result with QgsVectorFileWriter.writeAsVectorFormat, an error say me that "regroupee" is a string...

My code, in the end of the for loop :

        alg_params = {
        'CRS': None,
        'LAYERS': [regroupee, calculatrice['OUTPUT']],
        'OUTPUT': 'memory:merge'

        merge = processing.run('native:mergevectorlayers', alg_params, context=context, is_child_algorithm=True)
        regroupee = merge['OUTPUT']

    QgsVectorFileWriter.writeAsVectorFormat(regroupee, "I:/moulin_z/DONNEES/temp_us235/test_iteration_pyqgis/regroupee.shp", "UTF-8", crs.createFromId(2154), "ESRI Shapefile")

And the error message :

Traceback (most recent call last):
File "<string>", line 231, in processAlgorithm
TypeError: QgsVectorFileWriter.writeAsVectorFormat(): arguments did not 
match any overloaded call:
overload 1: argument 1 has unexpected type 'str'
overload 2: argument 1 has unexpected type 'str'
overload 3: argument 1 has unexpected type 'str'

How can I export the final result as a shapefile ?

1 Answer 1


The error in this case is because, you don't have a QgsVectorLayer inside the ['OUTPUT'].

First, you have to verify the regrouppe have a QgsVectorLayer in the ['OUTPUT'] with:


Then when you verify that you have QGsVectorLayer, you can try with this line:

QgsVectorFileWriter.writeAsVectorFormat(regroupee, "I:/moulin_z/DONNEES/temp_us235/test_iteration_pyqgis/regroupee.shp", "UTF-8", QgsCoordinateReferenceSystem(2154, QgsCoordinateReferenceSystem.EpsgCrsId), "ESRI Shapefile")

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