import Blender
import sys
import bpy

bl_addon_info = {
    "name": "Save and Set Render Path",
    "author": "tmas",
    "version": (0,1),
    "blender": (2, 5, 6),
    "description": "Stops blender renders from overwriting each other",
    "category": "Tmas"}

class saveAndSetPath(bpy.types.Operator) :
    bl_idname = "file.saveandsetpath"
    bl_label = "Save and Set Renser
    def saveAndSetPath:
        bpy.ops.wm.save_mainfile(check_existing=False)
        filename = Blender.Get('filename')
        basename=Blender.sys.basename(filename)
        bpy.data.scenes[0].render.filepath = "D:\Renders\" + str(basename)