TypeError：'NoneType'对象不可迭代。 （arcpy.ListFeatureClasses）

Question

我正在尝试将任何未知的投影形状文件更改为  “NAD 1983 Alaska Albers”投影。

# import arcypy and from arcpy, import os to change directory
import arcpy
from arcpy import os

# set working directory to workspace 
os.chdir('C://Users/Elvis/Desktop/Spring/Geog376/Lab03/erase')

# Copy all dataset in working directory ###Need to change this back into my s drive
arcpy.CopyFeatures_management('C://Users/Elvis/Desktop/Spring/Geog376/Lab03/lab03_data/2004  _af.shp','C://Users/Elvis/Desktop/Spring/Geog376/Lab03/erase/2004_af.shp')
arcpy.CopyFeatures_management('C://Users/Elvis/Desktop/Spring/Geog376/Lab03/lab03_data/2004perimeters.shp','C://Users/Elvis/Desktop/Spring/Geog376/Lab03/erase/2004perimeters.shp')
arcpy.CopyFeatures_management('C://Users/Elvis/Desktop/Spring/Geog376/Lab03/lab03_data/AK_tundra.shp','C://Users/Elvis/Desktop/Spring/Geog376/Lab03/erase/AK_tundra.shp')
arcpy.CopyFeatures_management('C://Users/Elvis/Desktop/Spring/Geog376/Lab03/lab03_data/AK_taiga.shp','C://Users/Elvis/Desktop/Spring/Geog376/Lab03/erase/AK_taiga.shp')

# find what projection 2004_af.shp, 2004perimets.shp, AK_tundra, and AK_taiga.shp
# change the projections to the correct one (2004_af.shp)

# 2004_af.shp
desc_af =      arcpy.Describe('C://Users/Elvis/Desktop/Spring/Geog376/Lab03/erase/2004_af.shp')
sr_af = desc_af.spatialReference
print "projection name: "+sr_af.PCSname


# 2004perimeters.shp
desc_perimeters =    arcpy.Describe('C://Users/Elvis/Desktop/Spring/Geog376/Lab03/erase/2004perimeters.shp')
sr_perimeters = desc_perimeters.spatialReference
print "projection name: "+sr_perimeters.PCSname

# AK_tundra.shp
desc_tundra = arcpy.Describe('C://Users/Elvis/Desktop/Spring/Geog376/Lab03/erase/AK_tundra.shp')
sr_tundra = desc_tundra.spatialReference
print "projection name: "+sr_tundra.PCSname

# AK_taiga.shp
desc_taiga = arcpy.Describe('C://Users/Elvis/Desktop/Spring/Geog376/Lab03/erase/AK_taiga.shp')
sr_taiga = desc_taiga.spatialReference
print "projection name: "+sr_taiga.PCSname


# Here is where I got an error: arcpy.ListFeatureClasses

for infc in arcpy.ListFeatureClasses('2004perimeters', 'AK_tundra', 'AK_taiga'):
    desc = arcpy.Describe(infc)
    if desc.spatialReference.PCSname == "Unknown":
        outfc = os.path.join('C://Users/Elvis/Desktop/Spring/Geog376/Lab03/erase', infc) 
        # Set output coordinate system
        outcs = arcpy.SpatialReference('NAD 1983 Alaska Albers')
        # run project tool
        arcpy.Project_management(arcpy.ListFeatureClasses(infc, outfc, outcs))
        # check messages
        print arcpy.GetMessages()

Answer 1

函数arcpy.ListFeatureClasses()提供当前工作空间中所有要素类的列表（可以使用arcpy.env.workspace获取或设置）。除非您要使用通配符，要素类型或特定地理数据库要素数据集过滤结果，否则它不需要任何参数。如果您引用help，您会看到传递给ListFeatureClasses的参数与其参数不一致。这就是为什么它会返回None，而您的for语句无法迭代None。如果您不需要进行任何过滤，则可以使用：

arcpy.env.workspace = 'C:/Users/Elvis/Desktop/Spring/Geog376/Lab03/erase'
for infc in arcpy.ListFeatureClasses():

如果您只想迭代三个特定数据集，那么只需显式设置它们（您仍然可以使用工作空间环境来保存自己不输入完整路径名称）：

arcpy.env.workspace = 'C:/Users/Elvis/Desktop/Spring/Geog376/Lab03/erase'
for infc in ['2004perimeters', 'AK_tundra', 'AK_taiga']:

ListFeatureClasses函数也不属于对Project的调用。此外，似乎项目工具无论如何都不是您需要的。 Project工具将数据从一个坐标系统投影到另一个坐标系。相反，请查看Define Projection工具。