我无法将我的数据附加到列表中

Question

我正在尝试将总面积附加到属性表中，并且它在没有任何错误消息的情况下运行。我不确定我做错了什么：

import os
import arcpy
import math
folderpath = 'C:\Users\Michaelf\Desktop\GEOG M173'
arcpy.env.workspace = folderpath
arcpy.env.overwriteOutput = True
input_shp = folderpath + r'\lower48_county_2012_election.shp'
equal_shape = folderpath + r'\project_lower48.shp'

projection = arcpy.SpatialReference('USA Contiguous Albers Equal Area Conic USGS')
arcpy.Project_management(input_shp, equal_shape, projection)
print 'step 1'

arcpy.CopyFeatures_management (input_shp, equal_shape)
tot_area = []

print "step 2"
fields = [
    ("totarea", "FLOAT"),
]

for field in fields:
    arcpy.AddField_management(equal_shape, "totarea")
print "step 3"

with arcpy.da.SearchCursor(equal_shape, ("OID@", "SHAPE@AREA")) as cursor:
    for row in cursor:
    print("Feature {0} has an area of {1}".format(row[0], row[1]))
print "step 4"

a_cursor = arcpy.SearchCursor(equal_shape)
for area in a_cursor:
    tot_area.append(area.totarea,)
print "step 5"

更新： wnnmaw 当我运行代码时，它会运行并打印特征/多边形区域的列表，但是当我打开 .shp 文件时，新列就在那里，并且没有任何数据附加到列表中。 ZWiki 当我打印列表时，它会返回一个巨大的 0 列表，就像属性表中列出的一样。在代码中，我将其归类为 FLOAT，但在 arcmap 属性表属性中，它仍然将其标识为 LONG，这可能是问题，因为答案是小数吗？

Answer 1

首先：您在添加该字段列表时遇到了数据类型问题。

这段代码只是添加了一个名为totarea 的字段，并没有对fields 列表中的数据做任何事情。

for field in fields:
    arcpy.AddField_management(equal_shape, "totarea")

改为：

fields = [("totarea", "FLOAT")]
for field in fields:
    arcpy.AddField_management(equal_shape, field[0], field[1])

---

其次：Use an UpdateCursor。搜索游标无法更改表的数据。

如果您想坚持使用该区域列表：

tot_area = []
with arcpy.da.SearchCursor(equal_shape, ("OID@", "SHAPE@AREA")) as cursor:
    for row in cursor:
        print("Feature {0} has an area of {1}".format(row[0], row[1]))
        tot_area.append(row[1])
print "step 4"

sum_area = sum(tot_area)
with arcpy.da.UpdateCursor(equal_shape, ["TOTAREA"]) as cursor:
    for row in cursor:
        row[0] = sum_area
        cursor.updateRow(row)
print "step 5"

或者只是在搜索光标时求和：

tot_area = 0
with arcpy.da.SearchCursor(equal_shape, ("OID@", "SHAPE@AREA")) as cursor:
    for row in cursor:
        print("Feature {0} has an area of {1}".format(row[0], row[1]))
        tot_area += row[1]
print "step 4"

with arcpy.da.UpdateCursor(equal_shape, ["TOTAREA"]) as cursor:
    for row in cursor:
        row[0] = tot_area
        cursor.updateRow(row)
print "step 5"