__import__('pkg_resources').declare_namespace(__name__)

文件:

project/
    setup.py
    proj_ex/
        __init__.py
        corecode.py

>>pip install xxx

安装包过程:
先找到setup.py

from setuptools import setup

setup(
    ...
    name_space_packages = ['proj_ex']
    ...
)

name_space_packages 指向核心代码包:proj_ex

# __init__.py

__import__("pkg_resources").declare_namespace(__name__)

(1) pkg_resources是一个安装包的工具
(2) _import_()加载导入,import的隐式版
(3) 此处的_name_指的是proj_ex
(4) corecode.py加载到proj_ex的命名空间之中

参考:
[1] https://stackoverflow.com/questions/7785944/what-does-import-pkg-resources-declare-namespace-name-do/37104834
[2] https://stackoverflow.com/questions/5064951/packaging-common-python-namespaces