Example Blender script for getting/setting UV edge selection for large meshes using NumPy and foreach_get/set

uv_edges_blender.py

# Author: Iyad Ahmed

import bpy

# importing numpy is slow for first time
import numpy as np


prev_mode = bpy.context.object.mode
bpy.ops.object.mode_set(mode="OBJECT")

bpy.context.object.update_from_editmode()

mesh = bpy.context.object.data
uv_map = mesh.uv_layers.active

nf = len(mesh.polygons)
nl = len(mesh.loops)

loop_start = np.zeros(nf, dtype=int)
mesh.polygons.foreach_get("loop_start", loop_start)

loop_total = np.zeros(nf, dtype=int)
mesh.polygons.foreach_get("loop_total", loop_total)

start_r = np.repeat(loop_start, loop_total)
total_r = np.repeat(loop_total, loop_total)

loop_indices = np.arange(nl, dtype=int)
loop_indices_next = (
    (loop_indices - start_r + 1) % total_r
) + start_r  # Wrap loop indices so it becomes cyclic
# Maybe there's a better way?

uv_verts = np.zeros(nl * 2)
uv_map.data.foreach_get("uv", uv_verts)
uv_verts.shape = nl, 2

a = uv_verts[loop_indices]
b = uv_verts[loop_indices_next]
v = a - b

# Original UV verts select state
o_sel = np.zeros(nl, dtype=bool)
uv_map.data.foreach_get("select", o_sel)

# Select short uv edges
sel = (v * v).sum(axis=1) < 0.005 ** 2

sel[loop_indices_next] = sel[loop_indices_next] | sel[loop_indices]
# OR-ing as edge AB is same as BA,
# we don't want a vertex that was selected to be unselected
# Untill Blender supports proper UV edge selection again
# probably after GSOC 2021

# New select state
n_sel = sel | o_sel  # Select new edges and keep already selected
# n_sel = (~sel) & o_sel                 # Uncomment to deselct edges instead
uv_map.data.foreach_set("select", n_sel)

bpy.ops.object.mode_set(mode=prev_mode)