Different line widths with canvas.create_line?

Does anyone have any idea why I get different line widths on the canvas in the following example?

from Tkinter import *
bigBoxSize = 150

class cFrame(Frame):
    def __init__(self, master, cwidth=450, cheight=450):
        Frame.__init__(self, master, relief=RAISED, height=550, width=600, bg = "grey")
        self.canvasWidth = cwidth
        self.canvasHeight = cheight
        self.canvas = Canvas(self, bg="white", width=cwidth, height=cheight, border =0)
        self.drawGridLines()
        self.canvas.pack(side=TOP, pady=20, padx=20)

    def drawGridLines(self, linewidth = 10):
        self.canvas.create_line(0, 0, self.canvasWidth, 0, width= linewidth )
        self.canvas.create_line(0, 0, 0, self.canvasHeight, width= linewidth )

        self.canvas.create_line(0, self.canvasHeight, self.canvasWidth + 2, self.canvasHeight, width= linewidth )
        self.canvas.create_line(self.canvasWidth, self.canvasHeight, self.canvasWidth, 1, width= linewidth )

        self.canvas.create_line(0, bigBoxSize, self.canvasWidth, bigBoxSize, width= linewidth )
        self.canvas.create_line(0, bigBoxSize * 2, self.canvasWidth, bigBoxSize * 2, width= linewidth)


root = Tk()
C = cFrame(root)
C.pack()
root.mainloop()

It's really frustrating me as I have no idea what's happening. If anyone can help me out then that'd be fantastic. Th开发者_Python百科anks!

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When you draw a line with a width greater than 1, the extra pixels have to be drawn somewhere. As you observed in your own followup post, some of those pixels are being drawn off screen. All you need to do is adjust your original coordinates to take into account the width of the line.

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After some experimentation I think I see what's happening - some of the line on the left is being drawn outside the canvas which I think is really retarded. Is there anyway to draw the line so that the outer most bit of it is on the canvas? Alternatively, is there any easier way to draw a border around a widget or on the canvas?