Remove duplicate lines in a list, Python

Hi 

I'm trying to remove duplicate lines in a list using a Python script in Grasshopper. I'm using start and end points to check for equality. Two lines are considered equal if 1) they have the same start and end points  or 2) One lines start point is equal to the another lines' end point and the end point of the first line is start point of the second line. I get a runtime error which I couldn't figure out:

import rhinoscriptsyntax as rs

for i in range(0,len(lns)):

....for nxtLine in lns:

........if ((rs.CurveEndPoint(lns[i]) == rs.CurveEndPoint(nxtLine)) and

........(rs.CurveStartPoint(lns[i]) == rs.CurveStartPoint(nxtLine))) or

........((rs.CurveEndPoints(lns[i]) == rs.CurveStartPoint(nxtLine)) and

........(rs.CurveStartPoint(lns[i]) == rs.CurveEndPoint(nxtLine))):
............del nxtLine

Here is the error:

Runtime error (TypeErrorException): len() of unsized object
Traceback:
line 3, in script

My input is a list of curves called "lns".

Thanks