How to Import python package from another directory?

I have a project that is structured as follows:

project
├── api
│   ├── __init__.py
│   └── api.py
├── instance
│   ├── __init__.py
│   └── config.py
├── package
│   ├── __init__.py
│   └── app.py
├── requirements.txt
└── tests
    └── __init__.py

I am trying to call the config.py file from the package/app.py as shown below:

# package/app.py
from instance import config

# I've also tried
import instance.config
import ..instance.config
from ..instance import config

But I always get the following error:

Traceback (most recent call last):
  File "/home/csymvoul/projects/project/package/app.py", line 1, in <module>
    from instance import config
ModuleNotFoundError: No module named 'instance'

Modifying the sys.path is not something I want to do. I know that this question is very much answered but the answers that were given, did not work for me.

EDIT: When moving the app.py to the root folder it works just fine. But I need to have it under the package folder.

Solution

You can add the parent directory to PYTHONPATH, in order to achieve that, you can use OS depending path in the "module search path" which is listed in sys.path. So you can easily add the parent directory like following:

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

from instance import config

Note that the previous code uses a relative path, so you must launch the file inside the same location or it will likely not work. To launch from anywhere, you can use the pathlib module.

from pathlib import Path
import sys
path = str(Path(Path(__file__).parent.absolute()).parent.absolute())
sys.path.insert(0, path)

from instance import config

However, the previous approach is more a hack than anything, in order to do things right, you'll first need to reshape your project structure according to this very detailed blog post python packaging, going for the recommended way with a src folder.

Your directory layout must look like this:

project
├── CHANGELOG.rst
├── README.rst
├── requirements.txt
├── setup.py
├── src
│   ├── api
│   │   ├── api.py
│   │   └── __init__.py
│   ├── instance
│   │   ├── config.py
│   │   └── __init__.py
│   └── package
│       ├── app.py
│       └── __init__.py
└── tests
    └── __init__.py

Note that you don't really need the requirements.txt because you can declare the dependencies inside your setup.py. A sample setup.py (adapted from here):

#!/usr/bin/env python
# -*- encoding: utf-8 -*-
from __future__ import absolute_import
from __future__ import print_function

import io
import re
from glob import glob
from os.path import basename
from os.path import dirname
from os.path import join
from os.path import splitext

from setuptools import find_packages
from setuptools import setup


def read(*names, **kwargs):
    with io.open(
        join(dirname(__file__), *names),
        encoding=kwargs.get('encoding', 'utf8')
    ) as fh:
        return fh.read()


setup(
    name='nameless',
    version='1.644.11',
    license='BSD-2-Clause',
    description='An example package. Generated with cookiecutter-pylibrary.',
    author='mpr',
    author_email='contact@ionelmc.ro',
    packages=find_packages('src'),
    package_dir={'': 'src'},
    include_package_data=True,
    zip_safe=False,
    classifiers=[
        # complete classifier list: http://pypi.python.org/pypi?%3Aaction=list_classifiers
        'Development Status :: 5 - Production/Stable',
        'Intended Audience :: Developers',
        'License :: OSI Approved :: BSD License',
        'Operating System :: Unix',
        'Operating System :: POSIX',
        'Operating System :: Microsoft :: Windows',
        'Programming Language :: Python',
        'Programming Language :: Python :: 2.7',
        'Programming Language :: Python :: 3',
        'Programming Language :: Python :: 3.5',
        'Programming Language :: Python :: 3.6',
        'Programming Language :: Python :: 3.7',
        'Programming Language :: Python :: 3.8',
        'Programming Language :: Python :: Implementation :: CPython',
        'Programming Language :: Python :: Implementation :: PyPy',
        # uncomment if you test on these interpreters:
        # 'Programming Language :: Python :: Implementation :: IronPython',
        # 'Programming Language :: Python :: Implementation :: Jython',
        # 'Programming Language :: Python :: Implementation :: Stackless',
        'Topic :: Utilities',
    ],
    keywords=[
        # eg: 'keyword1', 'keyword2', 'keyword3',
    ],
    python_requires='>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*',
    install_requires=[
        # eg: 'aspectlib==1.1.1', 'six>=1.7',
    ],
    extras_require={
        # eg:
        #   'rst': ['docutils>=0.11'],
        #   ':python_version=="2.6"': ['argparse'],
    },
    setup_requires=[
        # 'pytest-runner',
    ],
    entry_points={
        'console_scripts': [
            'api = api.api:main',
        ]
    },
)

The content of my api.py:

from instance import config

def main():
    print("imported")
    config.config()

The content of my config.py:

def config():
    print("config imported successfully")

You can find all the previous here

Optional but recommended: create a virtual environment, I use venv (Python 3.3 <=) for that, inside the root of the project:

python -m venv .

And to activate:

source bin/activate

Now I can install the package:

Using pip install -e . (with the dot) command inside the root of the project

Your import from instance import config works now, to confirm you can run api.py with:

python src/api/api.py