import bpy
import bmesh

def main(context):

    context = bpy.context
    ob = context.edit_object
    me = ob.data
    bm = bmesh.from_edit_mesh(me)

    bpy.ops.mesh.select_mode(use_extend=False, use_expand=False, type='EDGE')

    originalEdges = set(e for e in bm.edges if e.select)

    bpy.ops.mesh.poke()

    allEdges = set(e for e in bm.edges if e.select)

    bpy.ops.mesh.region_to_loop()

    borderEdges = set(e for e in bm.edges if e.select)

    diamondEdges = allEdges - originalEdges - borderEdges

    originalWithoutBorder = originalEdges - borderEdges

    bpy.ops.mesh.select_all(action='DESELECT')

    for e in originalWithoutBorder:
       e.select = True

    bpy.ops.mesh.dissolve_mode(use_verts=True)

    for e in diamondEdges:
        e.select = True

    bpy.ops.mesh.select_mode(use_extend=False, use_expand=False, type='VERT')
    bpy.ops.mesh.select_mode(use_extend=False, use_expand=False, type='FACE')

    newFaces = set(f for f in bm.faces if f.select)
    bpy.ops.mesh.select_face_by_sides(number=3, type='EQUAL', extend=False)
    triangleFaces = set(f for f in bm.faces if f.select)

    newFaces = newFaces - triangleFaces
    bpy.ops.mesh.select_all(action='DESELECT')
    for f in newFaces:
       f.select = True

    bmesh.update_edit_mesh(me)

class VitalyPoke(bpy.types.Operator):

    """

    [Vitaly Poke]

    Description:
    Uses the Poke operator and some caveman code to convert a selection of quads into diamond-looking faces

    """

    bl_idname = "arc.vitaly_poke"
    bl_label = "Vitaly Poke (ARC)"

    @classmethod
    def poll(cls, context):
        return context.active_object is not None

    def execute(self, context):
        main(context)
        return {'FINISHED'}

def register():
    bpy.utils.register_class(VitalyPoke)

def unregister():
    bpy.utils.unregister_class(VitalyPoke)

if __name__ == "__main__":
    register()