updated code in a few files to make it more understandable, also used .join method at a place to increase the speed.

toolboxes/STLtoVoxel/perimeter.py

@@ -36,12 +36,11 @@ def generate_y(p1, p2, x):
 
 def paint_y_axis(lines, pixels, x):
     is_black = False
-    target_ys = list(map(lambda line: int(generate_y(line[0], line[1], x)), lines))
-    target_ys.sort()
+    target_ys = sorted(
+        map(lambda line: int(generate_y(line[0], line[1], x)), lines)
+    )
     if len(target_ys) % 2:
-        distances = []
-        for i in range(len(target_ys) - 1):
-            distances.append(target_ys[i+1] - target_ys[i])
+        distances = [target_ys[i+1] - target_ys[i] for i in range(len(target_ys) - 1)]
         # https://stackoverflow.com/a/17952763
         min_idx = -min((x, -i) for i, x in enumerate(distances))[1]
         del target_ys[min_idx]
@@ -54,7 +53,7 @@ def paint_y_axis(lines, pixels, x):
         pixels[target_y][x] = True
         is_black = not is_black
         yi = target_y
-    assert is_black is False, 'an error has occured at x%s' % x
+    assert is_black is False, f'an error has occured at x{x}'
 
 
 def generate_line_events(line_list):

toolboxes/STLtoVoxel/slice.py

@@ -1,3 +1,4 @@
+import itertools
 import multiprocessing as mp
 import sys
 
@@ -90,10 +91,7 @@ def triangle_to_intersecting_lines(triangle, height, pixels, lines):
             y = int(same[0][1])
             pixels[y][x] = True
     else:
-        cross_lines = []
-        for a in above:
-            for b in below:
-                cross_lines.append((b, a))
+        cross_lines = [(b, a) for a, b in itertools.product(above, below)]
         side1 = where_line_crosses_z(cross_lines[0][0], cross_lines[0][1], height)
         side2 = where_line_crosses_z(cross_lines[1][0], cross_lines[1][1], height)
         lines.append((side1, side2))