Post #670: 
Leafar:
Hi everyone! I have this script:
Now I want to select the separated mesh and go to edit mode of that mesh but I do not know how I can do that! Any help? XD
Cool tool. Try this code in Command tab:
from .bl_utils import uname; new_name = uname(D.objects, C.active_object.name); bpy.ops.mesh.separate(type='SELECTED'); bpy.ops.object.mode_set(mode='OBJECT'); bpy.ops.object.select_all(action='DESELECT'); C.scene.objects.active = D.objects[new_name]; D.objects[new_name].select = True; bpy.ops.object.mode_set(mode='EDIT')