'Configure lineitem according to provided arguments:
coordlist is sequence of coordinates
fill is drawing color
width is width of drawn line.
top is a boolean value, which specifies if polyitem
will be put on top of the canvas\' displaylist so it
will not be covered by other items.'

def _drawline(self, lineitem, coordlist=None, fill=None, width=None, top=False):

    if (coordlist is not None):
        cl = []
        for (x, y) in coordlist:
            cl.append((x * self.xscale))
            cl.append(((- y) * self.yscale))
        self.cv.coords(lineitem, *cl)
    if (fill is not None):
        self.cv.itemconfigure(lineitem, fill=fill)
    if (width is not None):
        self.cv.itemconfigure(lineitem, width=width)
    if top:
        self.cv.tag_raise(lineitem)
