PyQGIS – Saving Layer as Shapefile

pyqgissaveshapefilevector-layerwriters

Using QGIS 3.4.4, I'm trying to save a layer as shapefile with the following code:

import os
import qgis.core

working_folder = r'C:\myFolder'
fc_Prospect = os.path.join(working_folder, Equipment.gdb|layername=Prospect) 
layer1 = QgsVectorLayer(fc_Prospect, 'Prospect', 'ogr')
       
path = r'C:\myFolder\test.shp'
_writer = QgsVectorFileWriter.writeAsVectorFormat(layer1,path,'utf-8','ESRI Shapefile')

However, I am getting this error:

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

I am quite new with python, so I am not sure what this error means. I've been checking documentation at https://qgis.org/pyqgis/master/core/QgsVectorFileWriter.html#qgis.core.QgsVectorFileWriter.writeAsVectorFormat, but it didn't really help.

Best Answer

Looking at the documentation suggests that it is expecting these parameters:

Parameters:

layer – layer to write

fileName – file name to write to

fileEncoding – encoding to use

destCRS – CRS to reproject exported geometries to, or invalid CRS for no reprojection

driverName – OGR driver to use

onlySelected – write only selected features of layer

errorMessage – pointer to buffer fo error message

datasourceOptions – list of OGR data source creation options

layerOptions – list of OGR layer creation options

skipAttributeCreation – only write geometries

newFilename – QString pointer which will contain the new file name created (in case it is different to fileName).

symbologyExport – symbology to export

symbologyScale – scale of symbology

filterExtent – if not a null pointer, only features intersecting the extent will be saved (added in QGIS 2.4)

overrideGeometryType – set to a valid geometry type to override the default geometry type for the layer. This paramet

So your error says it is expecting the 4th parameter to be a CRS not a string.

I suspect that means you should write your call as:

_writer = QgsVectorFileWriter.writeAsVectorFormat(layer1,path,'utf-8',driverName='ESRI Shapefile')

Related Solutions

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 3 – Setting QgsVectorFileWriter.SaveVectorOptions for QGIS 3

As it happens, I have just finished updating the documentation on vector layers. The big change is that you can't pass in None as the CRS any longer, so either use an explicit one or leave it out altogether.

You now need something like:

writer = QgsVectorFileWriter("my_shapes", "UTF-8", driverName="ESRI Shapefile")

The latest docs are available which give the full list of parameters.

Best Answer

Related Solutions

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

New

PyQGIS 3 – Setting QgsVectorFileWriter.SaveVectorOptions for QGIS 3

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