Loading a Shapefile in standalone PyQGIS script

Question

I am writing a script to validate a shapefile.

Here my code:

#-*- coding: UTF-8 -*-
import os
from osgeo import ogr
from PyQt4.QtGui import *
from qgis.core import *
import sys
app = QApplication([])
QgsApplication.setPrefixPath("/usr/", True) # Adjust prefix path according to your installation (see note below)
QgsApplication.initQgis()
class validacaoVetorialMCV(QgsVectorLayer):
 """docstring for Arquivo"""
 def __init__(self, arquivo_shp):
 self.arquivo_shp = arquivo_shp
 def campo_not_null(self, arquivo_shp):
 #Fields to check
 for value in ('geometriaA', 'regime', 'tipoTrecho', 'tipoMassaD', 'tipoLocali', 'jurisdicao', 'administra', 'nivel_1', 'nivel_2', 'nivel_3'):
 idx = arquivo_shp.fieldNameIndex(value);
 values = arquivo_shp.uniqueValues(idx);
 if all(x for x in values) == False:
 return 'Registros nulos em %s do: %s' (value, %arquivo_shp.name());
#rootdir = raw_input('Caminho da pasta:')
rootdir = '/home/infra/PycharmProjects/untitled/projeto_desenvolvimento_script/folha_mi_1584_2'
extensions = ('.shp')
for subdir, dirs, files in os.walk(rootdir):
 for file in files:
 ext = os.path.splitext(file)[-1].lower()
 #Print all files which have .shp extension
 if ext in extensions:
 #print os.path.join(subdir, file)
 layer = QgsVectorLayer(os.path.join(rootdir, file), file, "ogr")
 #Check if layer was setting
 print layer.name()
 if not layer.isValid():
 print "Layer failed to load!"
 print validacaoVetorialMCV(layer).validar_normalizacao_campo(layer)

Why does my method "campo_not_null" not work? Why did my layer failed to load? Why were other extensions that are not .shp (.gdb, timestamp) read?

Answer in python console:

mi_1584_2_cerrado.shp Layer failed to load! []
mi_1584_2_localidade.shp Layer failed to load! [] 
mi_1584_2_massa_dagua.shp Layer failed to load! [] 
mi_1584_2_trecho_massa_dagua.shp Layer failed to load! [] 
mi_1584_2_trecho_drenagem.shp Layer failed to load! [] 
mi_1584_2_trecho_rodoviario.shp Layer failed to load! [] 
timestamps Layer failed to load! [] 
gdb Layer failed to load! []

• gene: Why use pyqgis from outside for that ? There are many other pure Python modules without QGIS.
• Diogo Caribé: Yes, you are right. I began to write this script with pyqgis. So I continued. I thought to learn more about Qgis API.

Answer 1

I thought to learn more about Qgis API.

Why not use directly the Python console ?

for subdir, dirs, files in os.walk(rootdir):
 for file in files:
 if file.endswith(".shp"):
 layer = QgsVectorLayer(os.path.join(rootdir, file), os.path.splitext(file)[0], "ogr")
 layer.isValid()

Works, but if you have subdirectories in rootdir, the layers in the subdirectories are not valid, because of the path os.path.join(rootdir, file)

The solution is to use os.path.join(subdir, file)

class validacaoVetorialMCV(QgsVectorLayer):
 """docstring for Arquivo"""
 def __init__(self, arquivo_shp):
 self.arquivo_shp = arquivo_shp
 def campo_not_null(self):
 for value in ('IDENT','NUM'):
 idx = self.arquivo_shp.fieldNameIndex(value)
 values = self.arquivo_shp.uniqueValues(idx)
 if all(x for x in values) == False:
 return (value,layer.name())
for subdir, dirs, files in os.walk(rootdir):
 for file in files:
 if file.endswith(".shp"):
 layer = QgsVectorLayer( os.path.join(subdir, file), os.path.splitext(file)[0], "ogr")
 if layer.isValid(): 
 print validacaoVetorialMCV(layer).campo_not_null()