Mesh Editing and bmesh

Trigger

Use this skill when the user:

• Wants to create, modify, or read mesh geometry from Python
• Mentions bmesh, mesh.vertices, foreach_set, from_pydata, evaluated_get
• Has a script that's slow and uses bpy.ops.mesh.* in a loop
• Needs the mesh after modifiers (subdivision surface, mirror, geometry nodes) have been applied
• Asks why their bmesh script crashes on the second run
• Reads or writes sculpt automasking (use_automasking_*, mesh_automasking_settings) and hits AttributeError on 5.2

Three layers, three use cases

There are three ways to touch mesh data and each is right in a specific situation.

Layer 1: bpy.data.meshes and direct vertex/edge/face access