When PyQGIS script is run through console layer does not load successfully

Question

I made a small script to save a shapefile to disk. I want to run the script through console. When I run the script through QGIS IDE, it runs successfully. But when I run it through the QGIS Python command prompt it says layer failed to load successfully.

What am I doing wrong?

from qgis.core import *
import qgis.utils


_layer = QgsVectorLayer("C:/Arundhati/RadioSignal/MasterLine.shp", "MASTERLINE", "ogr")

if not _layer.isValid():
  print("Layer failed to load!")    
else:
    print("Layer was loaded successfully!")

_writer = QgsVectorFileWriter.writeAsVectorFormat(_layer,                                
                               "C:/Arundhati/RadioSignal/MasterLine12.shp",
                               'utf-8',
                               QgsCoordinateReferenceSystem(),
                               'ESRI Shapefile')

I run the above file through QGIS Python console like the following:

Additionally Python also crashes:

What Am I doing wrong?

How to run the same script from outside the QGIS environment.

Answer 1

First of all, you should review Using PyQGIS in standalone scripts for further information.

Also, try to run "OSGeo Shell" as @Oscar states.

According to the documentation, you need to change your code into (like) that:

from qgis.core import *

QgsApplication.setPrefixPath("C:/Program Files/QGIS 3.0", True)  ###

qgs = QgsApplication([], False) ###
qgs.initQgis() ###

_layer = QgsVectorLayer("C:/Arundhati/RadioSignal/MasterLine.shp", "MASTERLINE", "ogr")

if _layer.isValid(): print("Layer was loaded successfully!")
else:  print("Layer failed to load!")

_writer = QgsVectorFileWriter.writeAsVectorFormat(_layer,
                                                  "C:/Arundhati/RadioSignal/MasterLine12.shp",
                                                  'utf-8',
                                                  _layer.sourceCrs(),
                                                  'ESRI Shapefile')

qgs.exitQgis() ###

and run the script in OSGeo Shell:

C:\Program Files\QGIS 3.0\bin> python3.exe "C:\Arundhati\RadioSignal\QGIS_test.py"

If you get this error: Fatal Python error: initfsencoding: unable to load the file system codec, run py3_env.bat in OSGeo Shell, then run the command above again.