pythonBlenderRecalculateNormals

import os
import bpy

base_to_obj_dir = os.path.join('C:\\', 'mypath')

def reset_blend():
    # simply can be
    # bpy.ops.wm.open_mainfile(filepath=bpy.data.filepath)
    bpy.ops.wm.read_factory_settings()

    for scene in bpy.data.scenes:
        for obj in scene.objects:
            scene.objects.unlink(obj)

    # only worry about data in the startup scene
    for bpy_data_iter in (
            bpy.data.objects,
            bpy.data.meshes,
            bpy.data.lamps,
            bpy.data.cameras,
            ):
        for id_data in bpy_data_iter:
            bpy_data_iter.remove(id_data)

def main():
    path = os.path.join(base_to_obj_dir, "02828884")
    obj_list = sorted(os.listdir(path))

    # loop through the strings in obj_list and add the files to the scene
    for item in obj_list:
        reset_blend()
        source_to_file = os.path.join(path, item, "model.obj")
        target_to_file = os.path.join(path, item, "model_r.obj")
        bpy.ops.import_scene.obj(filepath=source_to_file)

        bpy.ops.import_scene.obj(filepath=source_to_file)
        obj_objects = bpy.context.selected_objects[:]
        #obj_objects = [ o for o in bpy.context.scene.objects if o.select ]
        print("Starting--------------------------------------------")
        for obj in obj_objects:
            bpy.ops.object.select_all(action='DESELECT')
            obj.select = True
            bpy.context.scene.objects.active = obj
            # go edit mode
            bpy.ops.object.mode_set(mode='EDIT')
            # select al faces
            bpy.ops.mesh.select_all(action='SELECT')
            # recalculate outside normals
            bpy.ops.mesh.normals_make_consistent(inside=False)
            # go object mode again
            bpy.ops.object.editmode_toggle()
        print("Ending--------------------------------------------")

        bpy.ops.export_scene.obj(filepath=target_to_file,use_materials=True)

if __name__ == "__main__":
    main()