PyQGIS Error – Troubleshooting QgsVectorFileWriter.writeAsVectorFormat() Argument Mismatch

pyqgispyqgis-3

The following code iterates through a folder of .xyz files and is supposed to copy them into another folder.

for file in glob.glob("*.xyz"):
    uri = "file:///" + inputDir +"/"+ file + "?type=csv&delimiter=%s&crs=%s&xField=%s&yField=%s" % (" ", crs, "field_1", "field_2")
    name = file.replace('.xyz', '')
    lyr = QgsVectorLayer(uri, name, "delimitedtext")
    outputPath = outDir + file
    QgsVectorFileWriter.writeAsVectorFormat(lyr, outputPath, 'utf-8', lyr.crs(), "CSV", layerOptions='GEOMETRY=AS_XYZ')

However, I get the following error message:

TypeError: QgsVectorFileWriter.writeAsVectorFormat(): arguments did not match any overloaded call: overload 1: argument 'layerOptions' has unexpected type 'str' overload 2: argument 4 has unexpected type 'QgsCoordinateReferenceSystem' overload 3: argument 3 has unexpected type 'str'

Traceback (most recent call last): File
"C:/Users/denni/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\Clip_XYZ\Clip_XYZ.py",
line 283, in run
self.moveFiles() File "C:/Users/denni/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\Clip_XYZ\Clip_XYZ.py",
line 251, in moveFiles
QgsVectorFileWriter.writeAsVectorFormat(lyr, outputPath, 'utf-8', lyr.crs(), "CSV", layerOptions='GEOMETRY=AS_XYZ') TypeError:
QgsVectorFileWriter.writeAsVectorFormat(): arguments did not match any
overloaded call: overload 1: argument 'layerOptions' has unexpected
type 'str' overload 2: argument 4 has unexpected type
'QgsCoordinateReferenceSystem' overload 3: argument 3 has unexpected
type 'str'

I don't understand the error. When I check the documentation, layerOptions is a str, argument 4 is the crs, and argument 3 is also a str.

Are the docs wrong? Or is there something else wrong with my code?

Best Answer

Ok, I found the answer. layerOptions expects a list of strings. Thus, layerOptions=['GEOMETRY=AS_XYZ']is correct.

I still don't get the error for overload 2 and 3 though. But now these errors don't appear anymore.

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PyQGIS Shapefile – How to Write the Result of PyQGIS to a Shapefile

When you use QgsZonalStatistics, the results are are automatically added to the shapefile (look at Problem with calculating QGIS Zonal Statistics MEAN or Estadística zonal con PyQGIS: clase QgsZonalStatistics)

 vLayer = QgsVectorLayer("a_polygon.shp","a_polygon.shp","ogr")
 path = "test.tif"
 zoneStat = QgsZonalStatistics(vLayer, path,"", 1, QgsZonalStatistics.All)
 zoneStat.calculateStatistics(None)

Detail

If you examine the functions in ZoneStat with see (equivalent of dir)

 from see import see
 see(zoneStat)
 hash()           help()           repr()           str()            .All
.Count           .Majority        .Max             .Mean
.Median          .Min             .Minority        .Range           .StDev
.Statistic()     .Statistics()    .Sum             .Variety
.calculateStatistics()

And I did not understand how do we get the values (QGIS Zonal Stats Plugin - Python Console - compute one specific statistic, QgsZonalStatistics Class Reference)

 zoneStat.Count
 1 # -> it's part of an enumeration 
 zoneStat.Mean
 4 # -> it's part of an enumeration

You can also use the QGIS Zonal Statistics tool from the Processing plugin (look at How to calculate zonal statistics from multi-band raster for each polygon using python?

But I also do not understand why you use QGIS from outside when there are pure Python modules for that as rasterstats with one polygon here

 from rasterstats import zonal_stats
 stats = zonal_stats("a_polygon.shp", "test.asc")
 print stats
 [{'count': 398, 'max': 261.95001220703125, 'mean': 227.95232019472363, 'min': 194.2899932861328}]
 print stats[0]['mean']
 227.952320195
 mean = stats[0]['mean']

And you can use Fiona to save the result to a new shapefile without the "complications" of PyQGIS from outside

 with fiona.open("a_polygon.shp") as input:
    # add the mean field to the schema of the resulting shapefile
    schema = input.schema
    schema['properties']['mean'] = 'float:10.4'
    with fiona.open('result.shp', 'w', 'ESRI Shapefile', schema) as output:
        for feature in input:
            feature['properties']['mean']= mean
            output.write(feature)

New

If there are two or many polygons in the shapefile,

the results are for example

stats = zonal_stats("polygons.shp", "test.asc")
[{'count': 398, 'max': 261.95001220703125, 'mean': 227.95232019472363, 'min': 194.2899932861328}, {'count': 267, 'max': 246.6300048828125, 'mean': 222.61079412453182, 'min': 197.07000732421875},....]
means = [stat['mean'] for stat in stats]
print means
[227.95232019472363, 222.61079412453182....]

And

with fiona.open("polygons.shp") as input:
    # add the mean field to the schema of the resulting shapefile
    schema = input.schema
    schema['properties']['mean'] = 'float:10.4'
    with fiona.open('result2.shp', 'w', 'ESRI Shapefile', schema) as output:
        for i, feature in enumerate(input):
            feature['properties']['mean']= means[i]
            output.write(feature)

PyQGIS – Fix QFileDialog.getSaveFileName() Error in QGIS Plugin Code

Try

self.dlg.lineEdit.setText(filename[0])

instead of

self.dlg.lineEdit.setText(filename)

Best Answer

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PyQGIS Shapefile – How to Write the Result of PyQGIS to a Shapefile

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PyQGIS – Fix QFileDialog.getSaveFileName() Error in QGIS Plugin Code

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