from PyQt4.QtCore import *

# easy 2 config vars
myPath = "/media/ymirsson/MyData/GIS/tmp/"
myPts = "test_coords.shp"
myLines = "test_lines.shp"
sortField = "No"
myCRS = "25832"

# load the points layer
myPtsLayer = QgsVectorLayer(myPath + myPts, "My Points", "ogr")

# field def. 4 lines-layer
fields = QgsFields()
fields.append(QgsField("id", QVariant.Int))
fields.append(QgsField("name", QVariant.String))

# create writer
writer = QgsVectorFileWriter(myPath + myLines, "utf-8", fields, QGis.WKBLineString, QgsCoordinateReferenceSystem(int(myCRS), QgsCoordinateReferenceSystem.EpsgCrsId), "ESRI Shapefile")

if writer.hasError() == QgsVectorFileWriter.NoError:
    # featureobject to list
    features = myPtsLayer.getFeatures()
    Points=([])
    for feature in features:
        geom = feature.geometry().asPoint()
        sortID = feature.attributes()[myPtsLayer.fieldNameIndex(sortField)]
        Points.append([sortID,geom])
    Points.sort()

    # create lines
    for i in range(1,len(Points)):
        Line = QgsFeature()
        Line.setGeometry(QgsGeometry.fromPolyline([Points[i-1][1], Points[i][1]]))
        Line.setAttributes([i,str(Points[i-1][0]) + " to " + str(Points[i][0])])
        writer.addFeature(Line)
    # don't forget the last one -.-
    Line = QgsFeature()
    Line.setGeometry(QgsGeometry.fromPolyline([Points[len(Points)-1][1], Points[0][1]]))
    Line.setAttributes([len(Points),str(Points[len(Points)-1][0]) + " to " + str(Points[0][0])])
    writer.addFeature(Line)

# flush 2 disk
del writer

# load both layers into qgis-project
QgsMapLayerRegistry.instance().addMapLayer(myPtsLayer)
QgsMapLayerRegistry.instance().addMapLayer(QgsVectorLayer(myPath + myLines, "My Lines", "ogr"))

print "Done .. "