Python relative imports testing my sanity

Question

EDIT: A circular dependency issue was the reason why from .. import auth didn't work, see my own answer below. Cheers to all.

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I'm dabbling with relative imports in Python while reorganizing some code and what should have taken 10 minutes is now taking untold amounts of time. Here's my file structure:

project/
       /__init__.py
       /application.py
       /lib/
           /__init__.py
           /auth.py
           /utils.py
           /views/
                 /__init__.py
                 /login_view.py
                 /test.py

In login_view.py I have:

from . import auth

which yields: ImportError: cannot import name auth

However this works:

from ..auth import untoken, req_auth_or_error

Which I don't understand: auth is only one level above login_view, why the .. and not .?

This also fails with the same error:

from .. import auth

In test.py I tried the following:

import types
from .. import *

def imports():
    for name, val in globals().items():
        if isinstance(val, types.ModuleType):
            print 'imported: ', val.__name__

imports()

which results in:

imported:  lib.utils
imported:  lib.views
imported:  types

... I'm at a loss as to why lib.auth is not imported. What am I doing wrong?

I'm running the code as such (the abs. path is /scratch/project/):

$ cd project/
$ ./application.py

Answer 1

The problem was a circular dependency one and not one of relative imports.

Indeed, .. is needed to load a module from the parent directory.

However somewhere in auth.py I had an import views.login_view. I believe that the from .. import auth in login_view.py tried to import the auth module as it was being loaded itself. This is probably why from ..auth import untoken works because those functions had already been loaded.

Answer 2

In Python a single dot in import represents the current package, NOT the current module.

Then every additional dot represents a new level of "parentness" (ok this word does not exist but I think it expresses well what I mean). So the behaviour you notice in your first case is just normal.

For your second case, I to reproduced your hierarchy with those contents:

application.py

lib.views import login_view

print("oh yeah")

login_view.py

lib.views import login_view

print("oh my god")

... and running application.py from the project directory does not cause any error. I get the following output:

$ python application.py 
oh my god
oh yeah

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However, adding a from lib.views import test (using the exact same test.py content you provided) in the application.py gives me the following output showing that some lib modules are not loaded:

$ python application.py 
oh my god
imported:  types
imported:  lib.views
imported:  lib.auth
oh yeah

The lib.utils module is missing :/

What I think is that since from .. import * names nothing: no package, no module, no function or variable or anything, the import statement simply imports nothing. TH displayed modules/packages are only the one which have been loaded earlier.

That said, there is a way to force a "correct" behaviour by using the __all__ magic variable, which defines which modules are loaded when using the splat import, in the lib/__init__.py file:

__all__ = ['auth', 'views', 'utils']

After doing this, running again the application.py file shows the following:

$ python application.py 
oh my god
imported:  types
imported:  lib.auth
imported:  lib.views
imported:  lib.utils
oh yeah

Answer 3

In the first case, from . import auth the . means the package views. That is why Python can't find it.

But, to avoid those problems is recommended that you use absolute import instead of relative imports.

Answer 4

What if you went up 1 more directory when importing?

from ... import auth