跨目录级导入模块
from ..xxfile import xxmodule #从上级目录中的xxfile中导入xxmodule import xxsub_dir.xxfile #从xxsub_dir文件夹中导入所有模块
执行时的命令
python -m pkg.tests.core_test #去最顶级执行
(refer) [http://stackoverflow.com/questions/11536764/how-to-fix-attempted-relative-import-in-non-package-even-with-init-py/27876800#27876800]