如何从包中导入包？

Question

I'm writing a little package and I'm trying to include a demo script within it as an example. However, I can't seem to import the package cleanly from within as though I was outside of it.

With a directory structure like:

trainer/
  __init__.py
  helper.py
  trainer.py
  [...more files...]
  demo.py

In demo.py I can't do from .. import trainer as it complains "Attempted relative import in non-package", despite the __init__.py . If I move the demo up a directory and import trainer it works fine, but I was trying to keep it together with the package.

The hack-looking import __init__ as trainer works, but eeeew.

Importing the various bits from all over the module directly also works, but makes for a messy example. Am I wholly misguided in my attempt or is there a better solution?

Answer 1

If you're trying to run demo.py as python demo.py , the problem that you're having is likely the same as here .

What's happening is that Python's relative import mechanism works by using the __name__ of the current module. When you execute a module directly, the __name__ gets set "__main__" regardless what the actual module name is. Thus, relative (in-package) imports don't work.

To remedy this, you can do the following:

• Execute demo.py as a module within a package , like so: python -m trainer.demo . This should fix the error, but you'll still be importing the trainer.py module instead of the package.

• Now add from __future__ import absolute_import to demo.py , which will cause your imports to be absolute-only by default, meaning that relative imports have to explicit (as in, from . import (...) ). This is force import trainer to import the entire top-level package, instead of the module.

Answer 2

The way you organize the files, demo.py becomes part of the package, which might or might not be what you want. You can organize your files a little differently, moving demo.py outside of the trainer directory:

TopDir/
    demo.py
    trainer/
    __init__.py
    helper.py
    trainer.py
    [... more files ...]

Then, demo.py can do something like:

from trainer import trainer, helper