The method listed below can be added to the Polymer class and called on an instance of this class to save an SVG representation of the polymer. It centres the image on a $500 \times 500$ pixel canvas and projects the monomer unit positions onto the $(x,y)$ plane.

def save_svg(self, svg_name="polymer.svg"):  # webonly
    canvas_width, canvas_height = 500, 500
    background_colour = "white"
    fo = open(svg_name, "w")
    print(
        f"""<?xml version="1.0" encoding="utf-8"?>
             <svg xmlns="http://www.w3.org/2000/svg"
                  xmlns:xlink="http://www.w3.org/1999/xlink"
                  width="{canvas_width}" height="{canvas_height}"
                  style="background: {background_colour}">""",
        file=fo,
    )

    ccx, ccy = canvas_width / 2, canvas_height / 2
    scale = 10

    x, y, z = zip(*self.xyz)
    xmin, xmax, ymin, ymax = min(x), max(x), min(y), max(y)
    dmax = max(xmax - xmin, ymax - ymin)
    scale = min(canvas_width, canvas_height) / dmax
    for i in range(1, self.N):
        x1, y1 = x[i - 1] * scale + ccx, y[i - 1] * scale + ccy
        x2, y2 = x[i] * scale + ccx, y[i] * scale + ccy
        print(
            f'<line x1="{x1:.1f}" y1="{y1:.1f}" x2="{x2:.1f}"'
            f' y2="{y2:.1f}" style="stroke: "black"; stroke-width: 2;"/>',
            file=fo
        )
    print("</svg>", file=fo)

An example output image is given below.

from polymer import Polymer
Polymer.save_svg = save_svg
N, a = 1000, 1.0
polymer = Polymer(N, a)
polymer.save_svg("polymer.svg")