animated line drawing

edit

For sure, see the animated plots documentation.

EDIT: here is a possible solution:

def drawlines(lines, ns, **options):
    r"""
    Input:
    - ``lines``: a list of lines, each line being defined
      by its endpoints as ``[(x1,y1), (x2,y2)]``
    - ``ns``: the number of division of each line for the 
      animation
    - ``**options``: any option to pass to the graphic 
      command ``line``, like ``color`` or ``thickness``
    """
    resu = []
    preceeding = Graphics()
    for li in lines:
        x1, y1 = li[0]
        x2, y2 = li[1]
        dx = float(x2 - x1)/float(ns)
        dy = float(y2 - y1)/float(ns)
        for i in range(ns):
            xx = x1 + (i+1)*dx
            yy = y1 + (i+1)*dy
            resu.append(preceeding + line([(x1,y1), (xx,yy)], **options))
        preceeding = resu[-1]
    return resu

anim = animate(drawlines([[(1,2), (3,4)],
                          [(3,4), (3,0)],
                          [(3,0), (1,2)]], 10, color='red', thickness=2),
               xmin=0, xmax=4, ymin=0, ymax=5)

anim.show(delay=5)

You can see it at work on SageMathCell.