python3找不到newt库freebsd

Question

newt库已安装在freebsd 11上

$ freebsd-version 
11.3-RELEASE-p6

$ pkg info | grep newt
newt-0.52.20_1                 Not Eriks Windowing Toolkit: console I/O handling library

python2.7可以找到该库，但是python3.6找不到该库

$ python3.6
Python 3.6.9 (default, Apr 23 2020, 02:13:26) 
[GCC 4.2.1 Compatible FreeBSD Clang 8.0.0 (tags/RELEASE_800/final 356365)] on freebsd11
Type "help", "copyright", "credits" or "license" for more information.
>>> import snack
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ModuleNotFoundError: No module named 'snack'
>>> 
$ python2.7
Python 2.7.16 (default, Apr 22 2020, 20:56:40) 
[GCC 4.2.1 Compatible FreeBSD Clang 8.0.0 (tags/RELEASE_800/final 356365)] on freebsd11
Type "help", "copyright", "credits" or "license" for more information.
>>> import snack
>>> 

我不太了解pythonX的路径处理如何工作。