Draft_Extend.py

from FreeCADGui import Selection
from FreeCAD import Base
from PyQt4 import QtCore
import DraftGeomUtils

def extend(line1,line2,nearpoint):
    '''extends a Draft Line to another line -very similar to extend command in AutoCAD and it's clones '''
    edge1=line1.Object.Shape.Edges[0]
    edge2=line2.Object.Shape.Edges[0]
    #boundary =edge1,line to extend = edge2,nearpoint catches nearest vertex on line to extend
    #find the intersection point first
    intpt = DraftGeomUtils.findIntersection(edge1,edge2,True,True)
    #find closest end point of line to extend
    closestpointindex = DraftGeomUtils.findClosest(nearpoint,line2.Object.Points)
    #extend the line from the closest point
    if closestpointindex==0:
        line2.Object.Start = ( intpt[0].x,intpt[0].y,intpt[0].z)
    else:
        line2.Object.End = ( intpt[0].x,intpt[0].y,intpt[0].z)

#selection stuff

class SelObserver:
    selected=False

    def addSelection(self, doc, object, sub, point):
        self.selected=True
        self.point=point


def QtWait(ms):
    "QtWait(ms) Wait some time, leaving QT do its job."
    timer=QtCore.QTimer()
    timer.setSingleShot(True)
    loop=QtCore.QEventLoop()
    QtCore.QObject.connect(timer,QtCore.SIGNAL("timeout()"),loop,QtCore.SLOT("quit()"))
    timer.start(ms)
    loop.exec_(QtCore.QEventLoop.AllEvents)

def wait4sel(gate):
    "wait4sel('gate') Wait for a selection filtered by the gate and return the clicked point"
    so=SelObserver()
    if (gate !=""):
        Selection.addSelectionGate(gate)
    Selection.addObserver(so)

    while (not so.selected):
        QtWait(100)

    Selection.removeSelectionGate()
    Selection.removeObserver(so)
    return so.point

Msg("Select boundary Edges\r\n")
pt=wait4sel("SELECT Part::Feature SUBELEMENT Edge")
theObject=Gui.Selection.getSelectionEx()[0]

Msg("Select line to extend\r\n")
pt2=wait4sel("SELECT Part::Feature SUBELEMENT Edge")
theObject2=Gui.Selection.getSelectionEx()[0]

extend(theObject,theObject2,Base.Vector(pt2))
App.activeDocument().recompute()