[Python] Tkinter: how to colorize the outline of a canvas rectangle?

I draw a rectangle on a Canvas:

canvas = Canvas(parent, cursor="cross")
rect = canvas.create_rectangle(20,20, 1, 1, fill="")


I only want to draw the border, leaving the interior transparent (that is why I set fill="" as mentioned here).

My problem:

I want the rectangle to have a red border. How can I do that?

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