flip.py

# This example assumes we have a mesh object in edit-mode

import bpy
import bmesh
from mathutils import Vector

# Get the active mesh
obj = bpy.context.edit_object
me = obj.data


# Get a BMesh representation
bm = bmesh.from_edit_mesh(me)

# Modify the BMesh, can do anything here...
faces = [f for f in bm.faces if f.select]
if len(faces) != 2:
    raise Exception("Invalid selection")

verts = [v for v in bm.verts if v.select]
if len(verts) != 6:
    raise Exception("Invalid selection")

central_verts = [v for v in verts if len([e for e in v.link_edges if e.select]) == 3]
if len(central_verts) != 2:
    raise Exception("Invalid selection")

new_verts = {}

for v in central_verts:
    edges = [e for e in v.link_edges if e.select]
    pos = v.co.copy()
    for e in edges:
        for ev in e.verts:
            if not (ev in central_verts):
                pos += ev.co - v.co
    new_v = bm.verts.new(pos)
    new_verts[v] = new_v    

for f in faces:
    new_vs = [new_verts[v] if v in new_verts else v for v in f.verts]
    bm.faces.new(new_vs)
    bm.faces.remove(f)    

remove_edges = []
for e in central_verts[0].link_edges:
    if not e.is_valid:
        continue
    flag = False
    if central_verts[1] in e.verts:
        flag = True
    if flag:
        remove_edges.append(e)
for e in remove_edges:
    bm.edges.remove(e)

for v in central_verts:
    if not v.is_valid:
        continue
    if len([e for e in v.link_edges if not e.select]) == 0:
        bm.verts.remove(v)

# Show the updates in the viewport
# and recalculate n-gon tessellation.
bmesh.update_edit_mesh(me, True)