#### firstly, import Polygon class ####
from shapely.geometry import MultiPolygon, Polygon
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# make polygon
thetas = np.linspace(0, 2 * np.pi, 360)
polygon_x = x[:,None] + r[:,None] * np.sin(thetas)
polygon_y = y[:,None] + r[:,None] * np.cos(thetas)

# list of convex hulls of subsequent circles
ps = [Polygon(i) for i in np.dstack((polygon_x, polygon_y))]

# list of convex hulls of subsequent circles
n = range(len(ps)-1)
convex_hulls = [MultiPolygon([ps[i], ps[i+1]]).convex_hull for i in n]

# Final polygon
polygons = cascaded_union(convex_hulls)