It seems there are already quite some questions here about relative import in python 3, but after going through many of them I still didn’t find the answer for my issue. so here is the question.

I have a package shown below

package/
   __init__.py
   A/
      __init__.py
      foo.py
   test_A/
      __init__.py
      test.py

and I have a single line in test.py:

from ..A import foo

now, I am in the folder of package, and I run

python -m test_A.test

I got message

"ValueError: attempted relative import beyond top-level package"

but if I am in the parent folder of package, e.g., I run:

cd ..
python -m package.test_A.test

everything is fine.

Now my question is: when I am in the folder of package, and I run the module inside the test_A sub-package as test_A.test, based on my understanding, ..A goes up only one level, which is still within the package folder, why it gives message saying beyond top-level package. What is exactly the reason that causes this error message?

EDIT: There are better/more coherent answers to this question in other questions:

• Sibling package imports
• Relative imports for the billionth time

Why doesn’t it work? It’s because python doesn’t record where a package was loaded from. So when you do python -m test_A.test, it basically just discards the knowledge that test_A.test is actually stored in package (i.e. package is not considered a package). Attempting from ..A import foo is trying to access information it doesn’t have any more (i.e. sibling directories of a loaded location). It’s conceptually similar to allowing from ..os import path in a file in math. This would be bad because you want the packages to be distinct. If they need to use something from another package, then they should refer to them globally with from os import path and let python work out where that is with $PATH and $PYTHONPATH.

When you use python -m package.test_A.test, then using from ..A import foo resolves just fine because it kept track of what’s in package and you’re just accessing a child directory of a loaded location.

Why doesn’t python consider the current working directory to be a package? NO CLUE, but gosh it would be useful.

import sys
sys.path.append("..") # Adds higher directory to python modules path.

Try this. Worked for me.

Assumption:
If you are in the package directory, A and test_A are separate packages.

Conclusion:
..A imports are only allowed within a package.

Further notes:
Making the relative imports only available within packages is useful if you want to force that packages can be placed on any path located on sys.path.

EDIT:

Am I the only one who thinks that this is insane!? Why in the world is the current working directory not considered to be a package? – Multihunter

The current working directory is usually located in sys.path. So, all files there are importable. This is behavior since Python 2 when packages did not yet exist. Making the running directory a package would allow imports of modules as “import .A” and as “import A” which then would be two different modules. Maybe this is an inconsistency to consider.

None of these solutions worked for me in 3.6, with a folder structure like:

package1/
    subpackage1/
        module1.py
package2/
    subpackage2/
        module2.py

My goal was to import from module1 into module2. What finally worked for me was, oddly enough:

import sys
sys.path.append(".")

Note the single dot as opposed to the two-dot solutions mentioned so far.

Edit: The following helped clarify this for me:

import os
print (os.getcwd())

In my case, the working directory was (unexpectedly) the root of the project.

from package.A import foo

I think it’s clearer than

import sys
sys.path.append("..")

As the most popular answer suggests, basically its because your PYTHONPATH or sys.path includes . but not your path to your package. And the relative import is relative to your current working directory, not the file where the import happens; oddly.

You could fix this by first changing your relative import to absolute and then either starting it with:

PYTHONPATH=/path/to/package python -m test_A.test

OR forcing the python path when called this way, because:

With python -m test_A.test you’re executing test_A/test.py with __name__ == '__main__' and __file__ == '/absolute/path/to/test_A/test.py'

That means that in test.py you could use your absolute import semi-protected in the main case condition and also do some one-time Python path manipulation:

from os import path
…
def main():
…
if __name__ == '__main__':
    import sys
    sys.path.append(path.join(path.dirname(__file__), '..'))
    from A import foo

    exit(main())

Edit: 2020-05-08: Is seems the website I quoted is no longer controlled by the person who wrote the advice, so I’m removing the link to the site. Thanks for letting me know baxx.

If someone’s still struggling a bit after the great answers already provided, I found advice on a website that no longer is available.

Essential quote from the site I mentioned:

“The same can be specified programmatically in this way:

import sys

sys.path.append(‘..’)

Of course the code above must be written before the other import statement.

It’s pretty obvious that it has to be this way, thinking on it after the fact. I was trying to use the sys.path.append(‘..’) in my tests, but ran into the issue posted by OP. By adding the import and sys.path defintion before my other imports, I was able to solve the problem.

if you have an __init__.py in an upper folder, you can initialize the import as import file/path as alias in that init file. Then you can use it on lower scripts as:

import alias

In my humble opinion, I understand this question in this way:

[CASE 1] When you start an absolute-import like

python -m test_A.test

or

import test_A.test

or

from test_A import test

you’re actually setting the import-anchor to be test_A, in other word, top-level package is test_A . So, when we have test.py do from ..A import xxx, you are escaping from the anchor, and Python does not allow this.

[CASE 2] When you do

python -m package.test_A.test

or

from package.test_A import test

your anchor becomes package, so package/test_A/test.py doing from ..A import xxx does not escape the anchor(still inside package folder), and Python happily accepts this.

In short:

• Absolute-import changes current anchor (=redefines what is the top-level package);
• Relative-import does not change the anchor but confines to it.

Furthermore, we can use full-qualified module name(FQMN) to inspect this problem.

Check FQMN in each case:

• [CASE2] test.__name__ = package.test_A.test
• [CASE1] test.__name__ = test_A.test

So, for CASE2, an from .. import xxx will result in a new module with FQMN=package.xxx, which is acceptable.

While for CASE1, the .. from within from .. import xxx will jump out of the starting node(anchor) of test_A, and this is NOT allowed by Python.

Not sure in python 2.x but in python 3.6, assuming you are trying to run the whole suite, you just have to use -t

-t, –top-level-directory directory Top level directory of project (defaults to start directory)

So, on a structure like

project_root
  |
  |----- my_module
  |          \
  |           \_____ my_class.py
  |
  \ tests
      \___ test_my_func.py

One could for example use:

python3 unittest discover -s /full_path/project_root/tests -t /full_path/project_root/

And still import the my_module.my_class without major dramas.