This script converts open and closed edge loops into polylines

Supported:
	 Polylines where each vert has no more then 2 edges attached to it.

release/scripts/mesh_edges2curves.py

@@ -0,0 +1,161 @@
+#!BPY
+""" Registration info for Blender menus:
+Name: 'Edges to Curve'
+Blender: 241
+Group: 'Mesh'
+Tip: 'Edges not used by a face are converted into polyline(s)'
+"""
+__author__ = ("Campbell Barton")
+__url__ = ("blender", "elysiun")
+__version__ = "1.0 2006/02/08"
+
+__bpydoc__ = """\
+This script converts open and closed edge loops into polylines
+
+Supported:<br>
+	 Polylines where each vert has no more then 2 edges attached to it.
+"""
+
+from Blender import *
+
+def sortPair(a,b):
+	return min(a,b), max(a,b)
+
+def polysFromMesh(me):
+	# a polyline is 2 
+	#polylines are a list
+	polyLines = []
+	
+	# Get edges not used by a face
+	edgeDict= dict([ (sortPair(ed.v1.index, ed.v2.index), ed) for ed in me.edges ])
+	for f in me.faces:
+		for i in xrange(len(f.v)):
+			key= sortPair(f.v[i].index, f.v[i-1].index)
+			try:
+				del edgeDict[key]
+			except:
+				pass
+	edges= edgeDict.values()
+	
+	
+	'''
+	# build vert connectivite
+	vertConnex= [list() for i in xrange(len(me.verts))]
+	for ed in edges:
+		i1= ed.v1.index
+		i2= ed.v2.index
+		vertConnex[i1].append(i2)
+		vertConnex[i2].append(i1)
+		
+		
+	# verts without 2 users are none.
+	vertConnex=[ [None,vc][len(vc)==2] for vc in vertConnex
+	'''
+
+	
+	while edges:
+		currentEdge= edges.pop()
+		startVert= currentEdge.v2
+		endVert= currentEdge.v1
+		polyLine= [startVert, endVert]
+		ok= 1
+		while ok:
+			ok= 0
+			#for i, ed in enumerate(edges):
+			i=len(edges)
+			while i:
+				i-=1
+				ed= edges[i]
+				if ed.v1 == endVert:
+					polyLine.append(ed.v2)
+					endVert= polyLine[-1]
+					ok=1
+					edges.pop(i)
+					#break
+				elif ed.v2 == endVert:
+					polyLine.append(ed.v1)
+					endVert= polyLine[-1]
+					ok=1
+					edges.pop(i)
+					#break
+				elif ed.v1 == startVert:
+					polyLine.insert(0, ed.v2)
+					startVert= polyLine[0]
+					ok=1
+					edges.pop(i)
+					#break	
+				elif ed.v2 == startVert:
+					polyLine.insert(0, ed.v1)
+					startVert= polyLine[0]
+					ok=1
+					edges.pop(i)
+					#break
+		polyLines.append((polyLine, polyLine[0]==polyLine[-1]))
+		print len(edges), len(polyLines)
+	return polyLines
+
+
+def mesh2polys():
+	scn= Scene.GetCurrent()
+	for ob in scn.getChildren():
+		ob.sel= 0
+	meshOb= scn.getActiveObject()
+	if meshOb==None or meshOb.getType() != 'Mesh':
+		Draw.PupMenu( 'ERROR: No Active Mesh Selected, Aborting' )
+		return
+	Window.WaitCursor(1)
+	Window.EditMode(0)
+	me = meshOb.getData(mesh=1)
+	polygons= polysFromMesh(me)
+	w=t=1
+	cu= Curve.New()
+	cu.setFlag(1)
+	ob= Object.New('Curve', me.name)
+	ob.link(cu)
+	scn.link(ob)
+	ob.Layers= meshOb.Layers
+	ob.setMatrix(meshOb.matrixWorld)
+	ob.sel= 1
+	i=0
+	for poly, closed in polygons:
+		if closed:
+			vIdx= 1
+		else:
+			vIdx= 0
+		
+		v= poly[vIdx]
+		cu.appendNurb([v.co.x, v.co.y, v.co.z, w, t])
+		cu[i].type= 0 # Poly Line
+		
+		# Close the polyline if its closed.
+		if closed:
+			cu[i].setFlagU(1)
+		
+		# Add all the points in the polyline.
+		while vIdx<len(poly):
+			v= poly[vIdx]
+			cu.appendPoint(i, [v.co.x, v.co.y, v.co.z, w])
+			vIdx+=1
+		i+=1
+	Window.WaitCursor(0)
+
+# not used as yet.
+"""
+def writepolys():
+	me = Scene.GetCurrent().getActiveObject().getData(mesh=1)
+	polygons= polysFromMesh(me)
+	file=open('/polygons.txt', 'w')
+	for ply in polygons:
+		file.write('polygon ')
+		if ply[1]:
+			file.write('closed ')
+		else:
+			file.write('open ')
+		file.write('%i\n' % len(ply[0]))
+		for pt in ply[0]:
+			file.write('%.6f %.6f %.6f\n' % tuple(pt.co) )
+	file.close()
+"""
+
+if __name__ == '__main__':
+	mesh2polys()