python - 被相对进口难倒

Question

我不知道发生了什么:

$ ls
__init__.py  main.py  module.py
$ cat main.py
from . import module
$ python3 main.py
Traceback (most recent call last):
  File "main.py", line 1, in <module>
    from . import module
ValueError: Attempted relative import in non-package

Answer 1

From PEP 328 :

Relative imports use a module's __name__ attribute to determine that module's position in the package hierarchy. If the module's name does not contain any package information (e.g. it is set to '__main__') then relative imports are resolved as if the module were a top level module, regardless of where the module is actually located on the file system.

说明:__name__ 属性通常是导入模块时的路径，例如在 foo/bar.py 中，如果 foo 是顶级包，则 __name__ 将为“foo.bar”。在您直接运行的 .py 文件的特殊情况下，__name__ 的计算结果为 '__main__'，这意味着相对导入将不起作用。