Modify pointnet_ops_lib successfully，but can not import new attribute

I have added some attributes to the sampling.cpp and sampling_gpu.cu and complied successfully,why can't it work?
```
out = _ext.farthest_point_sampling(xyz, weights, npoint)                            
AttributeError: module 'pointnet2_ops._ext' has no attribute 'farthest_point_sampling'
```
the farthest_point_sampling is the new attribute and I can use the old attributes.