AttributeError: module 'normalSpeed' has no attribute 'depth_normal'

[xiujiayun]

I get an error when I run the example：
AttributeError: module 'normalSpeed' has no attribute 'depth_normal'

[yyzzyy78]

I get the same error as follows:
Traceback (most recent call last):
File "./example.py", line 40, in
normals_map_out = normalSpeed.depth_normal(depth, fx, fy, k_size, distance_threshold, difference_threshold, point_into_surface)
AttributeError: module 'normalSpeed' has no attribute 'depth_normal'

I installed pybind11 from source code as:
cd pybind11 && mkdir build && cd build && cmake ..
sudo make install
pip3 install pybind11 --user

In bash:

cd normalSpeed
sudo /home/yy/anaconda3/.../env/bin/python3.6 setup.py install --user