附加到覆盖先前值的元组_Python开发问题-跟版网

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问题描述

我正在使用 arcpy 来获取形状文件的所有折线.SearchCursor 返回一个光标，以便我可以遍历形状文件的所有功能.问题是我想保存游标返回的所有对象以供以后使用.

I'm using arcpy to get all the polylines of a shape file. SearchCursor returns a cursor so that I can iterate over all the features of shape file. Problem is I want to save all the objects returned by cursor for later use.

import arcpy
from arcpy import env

env.workspace = r"C:GIS DataGIS data"

desc = arcpy.Describe("River.shp")
shapefieldname = desc.ShapeFieldName

rows = arcpy.SearchCursor("River.shp")

featureList = ()

for row in rows:
    feat = row.getValue(shapefieldname)

    featureList = featureList + (feat, )

    print "%i %i" % (featureList[-1].firstPoint.X, featureList[-1].firstPoint.Y)
    print "%i %i" % (featureList[-1].lastPoint.X, featureList[-1].lastPoint.Y)

    print

print "---------------------------------------------------------------"

for feat in featureList:
    print "%i %i" % (feat.firstPoint.X, feat.firstPoint.Y)
    print "%i %i" % (feat.lastPoint.X, feat.lastPoint.Y)
    print

元组应该包含游标返回的所有对象.但它只有最后一个元素重复 size 元组次数.

Tuple supposed to contain all the objects returned by cursor. But it has only the last elements repeated size of tuple number of times.

3610930 2135882 3611593 2134453

3610930 2135882 3611593 2134453

3611806 2134981 3611593 2134453

3614160 2136164 3617432 2131734

3611593 2134453 3617432 2131734

3617432 2131734 3620568 2127591

3620568 2127591 3620785 2127423

3617980 2126657 3620568 2127591

3616768 2129454 3617948 2126649

3617948 2126649 3617980 2126657

3615102 2128889 3617587 2126510

3617587 2126510 3617948 2126649

3617624 2126416 3617980 2126657

3613129 2128176 3615155 2125617

3615155 2125617 3617587 2126510

3615086 2125515 3615155 2125617

起初，我尝试过使用列表.当我使用append()"方法时，也为列表找到了相同的输出.由于 tuple 是不可变的数据结构，+ 怎么会覆盖 tuple 之前的所有元素呢?虽然这段代码是为 arcpy 编写的，但我猜问题不是 arcgis 特有的.

At first, I've tried this using list. Same output was also found for list when I've used 'append()' method. As tuple is immutable data structure, how can + overwrites all the previous elements of tuple. Although this code is written for arcpy, but I guess the problem isn't arcgis specific.

附加到覆盖先前值的元组

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