import bpy
from pathlib import Path

interval = 100
paths = sorted([str(path) for path in Path.cwd().glob('*.ply')])

scene = bpy.context.scene
scene.frame_start = 0
scene.frame_end = len(paths) * interval
scene.frame_current = 0
bpy.ops.object.select_all(action='DESELECT')

for i, path in enumerate(paths):
    bpy.ops.import_mesh.ply(filepath=path)
    next_obj = bpy.context.object
    if i == 0:
        base_obj = next_obj
        base_obj.select = True
        continue

    scene.objects.active = base_obj
    bpy.ops.object.join_shapes()

    key_blocks = bpy.data.meshes[base_obj.data.name].shape_keys.key_blocks
    key_block = key_blocks[-1]
    key_block.value = 0.0
    key_block.keyframe_insert(data_path='value')
    scene.frame_current = i * interval
    for kb in key_blocks:
        kb.value = 0.0
        kb.keyframe_insert(data_path='value')
    key_block.value = 1.0
    key_block.keyframe_insert(data_path='value')

    # Delete next obj
    bpy.ops.object.select_all(action='DESELECT')
    next_obj.select = True
    bpy.ops.object.delete()