print 语句永远不会在循环中执行

Question

在下面发布的代码中，第一个嵌套的 for 循环按预期显示日志或打印状态。 但后者嵌套了以k和l作为索引的循环，从不显示其中的日志或打印语句。 请让我知道为什么打印声明

                    print(str(x) + ",,,,,,,,,,,,,,,,,,," + str(y))

尽管polygonCoordinatesInEPSG25832包含值，但永远不会显示

python 代码：

    for feature in featuresArray:
        polygonCoordinatesInEPSG4326.append(WebServices.fetchCoordinateForForFeature(feature))
    for i in range(len(polygonCoordinatesInEPSG4326)):
        for j in range(len(polygonCoordinatesInEPSG4326[i])):
            lon = polygonCoordinatesInEPSG4326[i][j][0]
            lat = polygonCoordinatesInEPSG4326[i][j][1]
            x, y = transform(inputProj, outputProj, lon, lat)
            xy.append([x,y])
            print ("lon:" + str(lon) + "," + "lat:" + str(lat)  + "<=>" + "x:" + str(x) + "," + "y:" , str(y))
            print(str(x) + "," + str(y))
            print("xy[%d]: %s"%(len(xy)-1,str(xy[len(xy)-1])))
            print("\n")
        print("len(xy): %d"%(len(xy)))
        polygonCoordinatesInEPSG25832.append(xy)
        print("len(polygonCoordinatesInEPSG25832[%d]: %d"%(i,len(polygonCoordinatesInEPSG25832[i])))
        xy.clear()

    print("len(polygonCoordinatesInEPSG25832 = %d" %(len(polygonCoordinatesInEPSG25832)))
    for k in range(len(polygonCoordinatesInEPSG25832)):
        for l in range(len(polygonCoordinatesInEPSG25832[k])):
            x = polygonCoordinatesInEPSG25832[k][l][0]
            y = polygonCoordinatesInEPSG25832[k][l][1]
            print(str(x) + ",,,,,,,,,,,,,,,,,,," + str(y))

Answer 1

polygonCoordinatesInEPSG25832包含值，但polygonCoordinatesInEPSG25832[k]不包含。 你 append 它与xy但你没有取消链接它所以当你调用xy.clear()它变成空的。 尝试深拷贝它。