Demo for attributes in triangle, see https://github.com/drufat/triangle/issues/43

tri_attributes.py

import triangle
import numpy
import matplotlib.pyplot as plt

# monkey-patch triangle library to enable -A option (see what happens
# if do_patch is false)

do_patch = True

if do_patch:
    terms = triangle.tri.terms
    terms = terms + ( ('triangleattributelist', 'triangle_attributes'), )
    triangle.tri.translate_frw = {_0: _1 for _0, _1 in terms}
    triangle.tri.translate_inv = {_1: _0 for _0, _1 in terms}
    print('monkey-patched to convert triangleattributelist <=> triangle_attributes')


# arrays to fill in with input
vertices = []
segments = []
regions = []

# make a box with given dims and place given attribute at its center
def make_box(x, y, w, h, attribute):

    i = len(vertices)
    
    vertices.append([x,   y])
    vertices.append([x+w, y])
    vertices.append([x+w, y+h])
    vertices.append([x,   y+h])

    segments.append((i+0, i+1))
    segments.append((i+1, i+2))
    segments.append((i+2, i+3))
    segments.append((i+3, i+0))

    regions.append([x+0.5*w, y+0.5*h, attribute, 0])

# generate some input    
make_box(0, 0, 5, 5, 1)
make_box(1, 1, 3, 1, 2)
make_box(1, 3, 1, 1, 3)
make_box(3, 3, 1, 1, 4)

# convert to dictionary of numpy arrays
tri_input = dict(vertices=numpy.array(vertices),
                 segments=numpy.array(segments),
                 regions=numpy.array(regions))

# plot input to triangle library
triangle.plot(plt.axes(), **tri_input)

for x, y, attr, _ in regions:
    plt.plot(x, y, 'm.')
    plt.text(x, y, ' {:g}'.format(attr), color='m')

plt.savefig('tri_input.png')
print('wrote tri_input.png')

# triangulate with p (because PSLG) and A (to get attributes)
tri_output = triangle.triangulate(tri_input, 'pA')
        
# now plot the output
plt.clf()

triangle.plot(plt.axes(), **tri_output)

for tidx, attr in zip(tri_output['triangles'],
                      tri_output['triangle_attributes'].flatten()):
    tri_verts = tri_output['vertices'][tidx]
    x, y = tri_verts.mean(axis=0)
    plt.plot(x, y, 'm.')
    plt.text(x, y, ' {:g}'.format(attr), color='m')

plt.savefig('tri_output.png')
print('wrote tri_output.png')