Python QGIS：图层无法加载

Question

I am trying to load a QGIS vector layer from a SHP file in Python. Whenever I run it, layer.isValid() always returns False (or "Layer is not valid!" in this case). I'm not sure what I am doing wrong here, or if I have instantiated the QgsVectorLayer variable incorrectly.

import sys
import os
from qgis.core import *
import matplotlib.pyplot as plt
from matplotlib.path import Path
import matplotlib.patches as patches


QgsApplication.setPrefixPath("/usr", True)
qgs = QgsApplication(sys.argv, False)
qgs.initQgis()

layer=QgsVectorLayer("/Users/ANON/Desktop/MassShapeFiles/MassachusettsTownBoundaries.shp", "MassachusettsTownBoundaries", "ogr")
providers = QgsProviderRegistry.instance().providerList()
for provider in providers:
    print provider
if not layer.isValid():
    print "Layer failed to load!"
provider = layer.dataProvider()

Thank you!

Answer 1

I think your path is malformed. Looking to path structure I assume you are in a windows system, so your windows path should be:

"\\Users\\ANON\\Desktop\\MassShapeFiles\\MassachusettsTownBoundaries.shp"

with double backslash notation to avoid python misunderstandings

Answer 2

you are in windows system. but you have used qgis prefix path as linux system. Get the proper qgis prefix path from qgis python console by printing QgsApplication.showSettings.