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Named Tuples in Python (and some Cairo contexts)

From: andrew cooke <andrew@...>

Date: Wed, 22 Jul 2009 21:22:56 -0400

I knew these (named tuples) existed, but I'd somehow forgotten about
them.  Tonight I'm wondering how to improve the Python wrapper for
cairo (pycairo - http://cairographics.org/documentation/pycairo/ ) and
was wondering how best to represent colours - subclassing a named
tuple seems like a nice way to go -
http://docs.python.org/library/collections.html#collections.namedtuple

The other thing I'm doing to pycairo is adding contexts.  So here's a
nicer (imho) version of the spiral example (
http://pycairo.sourcearchive.com/documentation/1.8.4-3/spiral_8py-source.html
):


def spiral():

    width, height = 400, 300

    surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
    ctx = cairo.Context(surface)

    with cset(ctx,
              source_rgb=WHITE,
              operator=cairo.OPERATOR_SOURCE):
        ctx.paint()

    with cset(ctx,
              line_width=0.1,
              source_rgb=BLACK):
        ctx.rectangle(0.25, 0.25, 0.5, 0.5)
        ctx.stroke()

    wd = .02 * width
    hd = .02 * height
    width -= 2
    height -= 2

    with cset(ctx,
              source_rgb=BLUE):
        ctx.move_to(width + 1, 1 - hd)
        for i in range(9):
            ctx.rel_line_to (0, height - hd * (2 * i - 1))
            ctx.rel_line_to (- (width - wd * (2 *i)), 0)
            ctx.rel_line_to (0, - (height - hd * (2*i)))
            ctx.rel_line_to (width - wd * (2 * i + 1), 0)
        ctx.stroke()

    surface.write_to_png('spiral.png')

Andrew

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