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POAppending to a tuple overwriting previous values
 

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  1. POAppending to a tuple overwriting previous values
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    <p>I'm using arcpy to get all the polylines of a shape file. <code>SearchCursor</code> 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. </p> <pre><code>import arcpy from arcpy import env env.workspace = r"C:\GIS Data\GIS 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 </code></pre> <p>Tuple supposed to contain all the objects returned by cursor. But it has only the last elements repeated <code>size</code> of tuple number of times.</p> <blockquote> <p>3610930 2135882 3611593 2134453</p> <p>3611806 2134981 3611593 2134453</p> <p>3614160 2136164 3617432 2131734</p> <p>3611593 2134453 3617432 2131734</p> <p>3617432 2131734 3620568 2127591</p> <p>3620568 2127591 3620785 2127423</p> <p>3617980 2126657 3620568 2127591</p> <p>3616768 2129454 3617948 2126649</p> <p>3617948 2126649 3617980 2126657</p> <p>3615102 2128889 3617587 2126510</p> <p>3617587 2126510 3617948 2126649</p> <p>3617624 2126416 3617980 2126657</p> <p>3613129 2128176 3615155 2125617</p> <p>3615155 2125617 3617587 2126510</p> <p>3615086 2125515 3615155 2125617</p> <hr> <p>3615086 2125515 3615155 2125617</p> <p>3615086 2125515 3615155 2125617</p> <p>3615086 2125515 3615155 2125617</p> <p>3615086 2125515 3615155 2125617</p> <p>3615086 2125515 3615155 2125617</p> <p>3615086 2125515 3615155 2125617</p> <p>3615086 2125515 3615155 2125617</p> <p>3615086 2125515 3615155 2125617</p> <p>3615086 2125515 3615155 2125617</p> <p>3615086 2125515 3615155 2125617</p> <p>3615086 2125515 3615155 2125617</p> <p>3615086 2125515 3615155 2125617</p> <p>3615086 2125515 3615155 2125617</p> <p>3615086 2125515 3615155 2125617</p> <p>3615086 2125515 3615155 2125617</p> </blockquote> <p>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 <code>+</code> overwrites all the previous elements of tuple. Although this code is written for arcpy, but I guess the problem isn't arcgis specific.</p>
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    1. COThe problem is most likely in your `row.getValue(shapefieldname)` call, check what it is returning -- it is not in how your using tuples (or lists). The latter would be more efficient for this.
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