Error Loading Layer/Shapefile in a Standalone Python QGIS Application

Question

I tried loading a shapefile on Python using PyQgis API but to no avail. I double-checked the path to shapefile and found it to be correct. QGIS module also seems to be imported just fine. When I checked on the provider list in QgsRegistry, it returns nothing.

May I know what I'm missing or how I should troubleshoot?

I am using Ubuntu 12.04, QGIS 2.4.0 Chugiak and Python 2.7.3.

Following are my output and code:

/usr/bin/python2.7 /home/victorzhiyulee/IdeaProjects/Delineation/select_dun_calculate_print.py Application state: QGIS_PREFIX_PATH env var: Prefix: /usr/bin/qgis Plugin Path: /usr/bin/qgis/lib/qgis/plugins Package Data Path: /usr/bin/qgis/share/qgis Active Theme Name: Active Theme Path: :/images/themes// Default Theme Path: :/images/themes/default/ SVG Search Paths: /usr/bin/qgis/share/qgis/svg/ User DB Path: /usr/bin/qgis/share/qgis/resources/qgis.db

Provider List Could not find OGR provider! File exists; Path is correct ('/home/victorzhiyulee/Desktop/dun.shp', 'dun', 'ogr') Layer failed to load!

Process finished with exit code 0

__author__ = 'victorzhiyulee'
# Importing QGis API
# Importing OGR & OSR
import os
import sys
import PyQt4.QtCore
import PyQt4.QtGui
import qgis.core
import qgis.gui
from qgis.core import *
from qgis.gui import *
from osgeo import ogr, osr
from PyQt4.QtCore import *

# Supply path to the QGis resources on your PC
# noinspection PyTypeChecker
QgsApplication.setPrefixPath("/usr/bin/qgis", True)
# Load providers
QgsApplication.initQgis()
# Show setting of parameters
print QgsApplication.showSettings()

# Load vector layer
data_source = "/home/victorzhiyulee/Desktop/dun.shp"
layer_name = "dun"
provider_name = "ogr"
fileInfo = QFileInfo(data_source)

print('Provider List')
print(QgsProviderRegistry.instance().providerList())

r = QgsProviderRegistry.instance()
if not 'ogr' in r.providerList():
    print 'Could not find OGR provider!'
else:
    print 'Providers found ok!'
# Add layer to the registry
layer = QgsVectorLayer(data_source, fileInfo.fileName(), provider_name)
QgsMapLayerRegistry.instance().addMapLayer(layer)

if fileInfo.exists():
    print("File exists; Path is correct")
    print(data_source, layer_name, provider_name)
    layer = QgsVectorLayer(data_source, fileInfo.fileName(), provider_name)
    if not layer.isValid():
        print("Layer failed to load!")
    else:
        print("Yes, layer loads successfully")
    features = layer.getFeatures()
else:
    print("Check if your path is correct")
    QgsApplication.exitQgis()
iteration = layer.getFeatures()
for features in iteration:
    # Fetch attributes
    attris = features.attributes()
    print(attris)
QgsApplication.exitQgis()

Answer 1

Here some tips to fix your problem :

1. you need to arrange your import statement. import qgis libs before pyqt.
2. Use from qgis.core import* instead of import qgis.core wich is also not a good practice.
3. create an instance of QApplication([]) like app=QApplication([])
4. Exit from the application like QgsApplication.exitQgis()

So your code should looks like :

__author__ = 'victorzhiyulee'
# Importing QGis API
# Importing OGR & OSR
import os
import sys
from qgis.core import *
from qgis.gui import *
from PyQt4.QtCore import *
from PyQt4.QtGui import *
from osgeo import ogr, osr

# Supply path to the QGis resources on your PC
# noinspection PyTypeChecker
app = QApplication([])
QgsApplication.setPrefixPath("/usr/bin/qgis", True)
# Load providers
QgsApplication.initQgis()
# Show setting of parameters
print QgsApplication.showSettings()

# Load vector layer
data_source = "/home/victorzhiyulee/Desktop/dun.shp"
layer_name = "dun"
provider_name = "ogr"
fileInfo = QFileInfo(data_source)

print('Provider List')
print(QgsProviderRegistry.instance().providerList())

r = QgsProviderRegistry.instance()
if not 'ogr' in r.providerList():
    print 'Could not find OGR provider!'
else:
    print 'Providers found ok!'
# Add layer to the registry
layer = QgsVectorLayer(data_source, fileInfo.fileName(), provider_name)
QgsMapLayerRegistry.instance().addMapLayer(layer)

if fileInfo.exists():
    print("File exists; Path is correct")
    print(data_source, layer_name, provider_name)
    layer = QgsVectorLayer(data_source, fileInfo.fileName(), provider_name)
    if not layer.isValid():
        print("Layer failed to load!")
    else:
        print("Yes, layer loads successfully")
    features = layer.getFeatures()
else:
    print("Check if your path is correct")
    QgsApplication.exitQgis()
iteration = layer.getFeatures()
for features in iteration:
    # Fetch attributes
    attris = features.attributes()
    print(attris)

QgsApplication.exitQgis()

With this code adapt for Windows I get this output :

C:\OSGeo4W64\bin\python.exe C:/Deve/test.py
Application state:
QGIS_PREFIX_PATH env var:       C:\OSGeo4W64\apps\qgis
Prefix:     C:\OSGeo4W64\apps\qgis
Plugin Path:        C:\OSGeo4W64\apps\qgis/plugins
Package Data Path:  C:\OSGeo4W64\apps\qgis/.
Active Theme Name:  
Active Theme Path:  /themes\\icons/
Default Theme Path: :/images/themes/default/
SVG Search Paths:   C:\OSGeo4W64\apps\qgis/./svg/
User DB Path:   C:\OSGeo4W64\apps\qgis/./resources/qgis.db
Auth DB Path:   qgis-auth.db

Provider List
[u'DB2', u'WFS', u'arcgisfeatureserver', u'arcgismapserver', u'delimitedtext', u'gdal', u'gpx', u'memory', u'mssql', u'ogr', u'ows', u'postgres', u'spatialite', u'virtual', u'wcs', u'wms']
Providers found ok!
File exists; Path is correct
('E:\\Prestations\\LEM20171102_URB_plu_laia\\extract_zone.shp', 'extract_zone', 'ogr')
Yes, layer loads successfully
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