即使使用__init__.py，也如何解决“尝试以非软件包方式进行相对导入”

I’m trying to follow PEP 328, with the following directory structure:

pkg/
  __init__.py
  components/
    core.py
    __init__.py
  tests/
    core_test.py
    __init__.py

In core_test.py I have the following import statement

from ..components.core import GameLoopEvents

However, when I run, I get the following error:

tests$ python core_test.py 
Traceback (most recent call last):
  File "core_test.py", line 3, in <module>
    from ..components.core import GameLoopEvents
ValueError: Attempted relative import in non-package

Searching around I found “relative path not working even with __init__.py” and “Import a module from a relative path” but they didn’t help.

Is there anything I’m missing here?

Yes. You’re not using it as a package.

python -m pkg.tests.core_test

To elaborate on Ignacio Vazquez-Abrams’s answer:

The Python import mechanism works relative to the __name__ of the current file. When you execute a file directly, it doesn’t have its usual name, but has "__main__" as its name instead. So relative imports don’t work.

You can, as Igancio suggested, execute it using the -m option. If you have a part of your package that is meant to be run as a script, you can also use the __package__ attribute to tell that file what name it’s supposed to have in the package hierarchy.

See http://www.python.org/dev/peps/pep-0366/ for details.

You can use import components.core directly if you append the current directory to sys.path:

if __name__ == '__main__' and __package__ is None:
    from os import sys, path
    sys.path.append(path.dirname(path.dirname(path.abspath(__file__))))

It depends on how you want to launch your script.

If you want to launch your UnitTest from the command line in a classic way, that is:

python tests/core_test.py

Then, since in this case ‘components’ and ‘tests’ are siblings folders, you can import the relative module either using the insert or the append method of the sys.path module. Something like:

import sys
from os import path
sys.path.append( path.dirname( path.dirname( path.abspath(__file__) ) ) )
from components.core import GameLoopEvents

Otherwise, you can launch your script with the ‘-m’ argument (note that in this case, we are talking about a package, and thus you must not give the ‘.py’ extension), that is:

python -m pkg.tests.core_test

In such a case, you can simply use the relative import as you were doing:

from ..components.core import GameLoopEvents

You can finally mix the two approaches, so that your script will work no matter how it is called. For example:

if __name__ == '__main__':
    if __package__ is None:
        import sys
        from os import path
        sys.path.append( path.dirname( path.dirname( path.abspath(__file__) ) ) )
        from components.core import GameLoopEvents
    else:
        from ..components.core import GameLoopEvents

In core_test.py, do the following:

import sys
sys.path.append('../components')
from core import GameLoopEvents

If your use case is for running tests, and it seams that it is, then you can do the following. Instead of running your test script as python core_test.py use a testing framework such as pytest. Then on the command line you can enter

$$ py.test

That will run the tests in your directory. This gets around the issue of __name__ being __main__ that was pointed out by @BrenBarn. Next, put an empty __init__.py file into your test directory, this will make the test directory part of your package. Then you will be able to do

from ..components.core import GameLoopEvents

However, if you run your test script as a main program then things will fail once again. So just use the test runner. Maybe this also works with other test runners such as nosetests but i haven’t checked it. Hope this helps.

My quick-fix is to add the directory to the path:

import sys
sys.path.insert(0, '../components/')

Issue is with your testing method,

you tried python core_test.py

then you will get this error ValueError: Attempted relative import in non-package

Reason: you are testing your packaging from non-package source.

so test your module from package source.

if this is your project structure,

pkg/
  __init__.py
  components/
    core.py
    __init__.py
  tests/
    core_test.py
    __init__.py

cd pkg

python -m tests.core_test # dont use .py

or from outside pkg/

python -m pkg.tests.core_test

single . if you want to import from folder in same directory . for each step back add one more.

hi/
  hello.py
how.py

in how.py

from .hi import hello

incase if you want to import how from hello.py

from .. import how

Old thread. I found out that adding an __all__= ['submodule', ...] to the __init__.py file and then using the from <CURRENT_MODULE> import * in the target works fine.

You can use from pkg.components.core import GameLoopEvents, for example I use pycharm, the below is my project structure image, I just import from the root package, then it works:

As Paolo said, we have 2 invocation methods:

1) python -m tests.core_test
2) python tests/core_test.py

One difference between them is sys.path[0] string. Since the interpret will search sys.path when doing import, we can do with tests/core_test.py:

if __name__ == '__main__':
    import sys
    from pathlib import Path
    sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
    from components import core
    <other stuff>

And more after this, we can run core_test.py with other methods:

cd tests
python core_test.py
python -m core_test
...

Note, py36 tested only.

This approach worked for me and is less cluttered than some solutions:

try:
  from ..components.core import GameLoopEvents
except ValueError:
  from components.core import GameLoopEvents

The parent directory is in my PYTHONPATH, and there are __init__.py files in the parent directory and this directory.

The above always worked in python 2, but python 3 sometimes hit an ImportError or ModuleNotFoundError (the latter is new in python 3.6 and a subclass of ImportError), so the following tweak works for me in both python 2 and 3:

try:
  from ..components.core import GameLoopEvents
except ( ValueError, ImportError):
  from components.core import GameLoopEvents

Try this

import components
from components import *

If someone is looking for a workaround, I stumbled upon one. Here’s a bit of context. I wanted to test out one of the methods I’ve in a file. When I run it from within

if __name__ == "__main__":

it always complained of the relative imports. I tried to apply the above solutions, but failed to work, since there were many nested files, each with multiple imports.

Here’s what I did. I just created a launcher, an external program that would import necessary methods and call them. Though, not a great solution, it works.

Here’s one way which will piss off everyone but work pretty well. In tests run:

ln -s ../components components

Then just import components like you normally would.

This is very confusing, and if you are using IDE like pycharm, it’s little more confusing. What worked for me: 1. Make pycharm project settings (if you are running python from a VE or from python directory) 2. There is no wrong the way you defined. sometime it works with from folder1.file1 import class

if it does not work, use import folder1.file1 3. Your environment variable should be correctly mentioned in system or provide it in your command line argument.

Because your code contains if __name__ == "__main__", which doesn’t be imported as a package, you’d better use sys.path.append() to solve the problem.