Why does QGIS 3.2 “native:extractvertices” algorithm not work properly in standalone script?

Question

I execute standalone python code (almost identical to the code in the accepted answer):

The output file does not contain data, and I get this error message:

Warning 6: Normalized/laundered field name: 'vertex_index' to 'vertex_ind'
Warning 6: Normalized/laundered field name: 'vertex_part' to 'vertex_par'
Warning 6: Normalized/laundered field name: 'vertex_part_index' to 'vertex_p_1'

Process finished with exit code -1073741819 (0xC0000005)

Field name limitation is known shapefile issue, but why output file is empty and why I get exit code -1073741819 (0xC0000005)?

Here is input and output shapefiles:

________

What can cause this problem?

Here is the code:

import sys

from qgis.core import (
     QgsApplication,
     QgsProcessingFeedback,
     QgsVectorLayer
)
from qgis.analysis import QgsNativeAlgorithms

QgsApplication.setPrefixPath(r'C:\OSGeo4W64\apps\qgis', True)
qgs = QgsApplication([], False)
qgs.initQgis()

sys.path.append(r'C:\OSGeo4W64\apps\qgis\python\plugins')

import processing
from processing.core.Processing import Processing
Processing.initialize()
QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())

layer = QgsVectorLayer(r"G:\test\input.shp", 'my layer', 'ogr')
output = r"G:\test\output.shp"
params = {
    'INPUT': layer,
    'OUTPUT': output,
}
feedback = QgsProcessingFeedback()
res = processing.run("native:extractvertices", params, feedback=feedback)
print(res)

Answer 1

Based on my comments.

This is my py3-env.bat

@ECHO OFF 

set OSGEO4W_ROOT=C:\OSGeo4W64

@echo off
call "%OSGEO4W_ROOT%\bin\o4w_env.bat"
call "%OSGEO4W_ROOT%\bin\qt5_env.bat"
call "%OSGEO4W_ROOT%\bin\py3_env.bat"

@echo off
path %OSGEO4W_ROOT%\apps\qgis\bin;%PATH%
set GDAL_FILENAME_IS_UTF8=YES

set VSI_CACHE=TRUE
set VSI_CACHE_SIZE=1000000
set QT_PLUGIN_PATH=%OSGEO4W_ROOT%\apps\qgis\qtplugins;%OSGEO4W_ROOT%\apps\qt5\plugins

SET PYCHARM="C:\Program Files\JetBrains\PyCharm 2018.1.4\bin\pycharm64.exe"

set PYTHONPATH=%OSGEO4W_ROOT%\apps\qgis\python
set PYTHONHOME=%OSGEO4W_ROOT%\apps\Python36
set PYTHONPATH=%OSGEO4W_ROOT%\apps\Python36\lib\site-packages;%PYTHONPATH%

set QT_QPA_PLATFORM_PLUGIN_PATH=%OSGEO4W_ROOT%\apps\Qt5\plugins\platforms
set QGIS_PREFIX_PATH=%OSGEO4W_ROOT%\apps\qgis


cd /d %~dp0
::python3 extractvertices_standalone.py
::pause
start "PyCharm aware of QGIS" /B %PYCHARM% %*

if execute the file directly from .bat work,and if open pycharm.This is my project using the osge4w python interpreter

Run and pycharm console show :

{'OUTPUT': 'C:\datos\output\output.shp'}

Open the file to see the result in QGIS.

Finally the standalone script,it's just like his worst simply by using my shapefiles

#native:extractvertices
import sys

from qgis.core import (
     QgsApplication,
     QgsProcessingFeedback,
     QgsVectorLayer
)
from qgis.analysis import QgsNativeAlgorithms

QgsApplication.setPrefixPath(r'C:\OSGeo4W64\apps\qgis', True)
qgs = QgsApplication([], False)
qgs.initQgis()

sys.path.append(r'C:\OSGeo4W64\apps\qgis\python\plugins')

import processing
from processing.core.Processing import Processing
Processing.initialize()
QgsApplication.processingRegistry().addProvider(QgsNativeAlgorithms())

layer = QgsVectorLayer(r"C:\datos\shapefiles\regions.shp", 'my layer', 'ogr')
output = r"C:\datos\output\output.shp"
params = {
    'INPUT': layer,
    'OUTPUT': output,
}
feedback = QgsProcessingFeedback()
res = processing.run("native:extractvertices", params, feedback=feedback)
print(res)

Tested using Windows 10 and QGIS 3.2

I hope this helps you

Answer 2

If you are running the algorithm in a standalone application, the standard error reporting does not work because the app to handle this is not there.

What you can do is:

1. Run the same algorithm inside QGIS and check what kind of error it reports

2. If that doesn't work (some things from the environment might have an influence...) you can also add your own progress handler in the standalone script which will produce additional feedback.

---

import logging
import sys
from qgis.core import QgsProcessingFeedback

class QgsLoggingFeedback(QgsProcessingFeedback):

    def __init__(self):
        super().__init__()
        self.handler = logging.StreamHandler(sys.stdout)
        # Also show INFO and DEBUG messages
        # self.handler.setLevel(logging.DEBUG)
        logging.getLogger().addHandler(self.handler)

    def reportError(self, msg, fatalError=False):
        logging.log(logging.ERROR, msg)

    def setProgressText(self, text):
        logging.log(logging.INFO, msg)

    def pushInfo(self, info):
        super().pushInfo(info)

    def pushCommandInfo(self, info):
        super().pushCommandInfo(info)

    def pushDebugInfo(self, info):
        super().pushDebugInfo(info)

    def pushConsoleInfo(self, info):
        super().pushConsoleInfo(info)


feedback = QgsLoggingFeedback()
res = processing.run("native:extractvertices", params, feedback=feedback)