Import files from a different folder in Python

David Y.

The Problem

How do I import local Python scripts in different folders?

The Solution

How we import Python scripts will depend on the directory structure we’re working with. There are different methods for importing scripts in child directories, parent directories, or sibling directories.

Let’s say we have the following directory structure:

/project
    main.py
    /lib
        /special
            specialfunctions.py
        libfunctions.py
    /app
        appfunctions.py

We should be able to import functions from any one of these scripts to any other. As we’ll see below, importing from child directories is quite straightforward whereas importing from parent or sibling directories is more complex.

Importing From Child Directories

To import functions from libfunctions.py into main.py, we can use the following import statement:

from lib.libfunctions import *

Similar syntax can be used to import from appfunctions.py:

from app.appfunctions import *

To import from specialfunctions.py, we add its containing subdirectory to our import path:

from lib.special.specialfunctions import *

Importing From Parent or Sibling Directories With Package Relative Imports

To import scripts from parent or sibling directories, we can use package relative imports. First, we must ensure that our directories are recognized as packages by Python, which we can do by creating an empty file named __init__.py in each of them.

/project
    main.py
    __init__.py
    /lib
        /special
            specialfunctions.py
            __init__.py
        libfunctions.py
        __init__.py
    /app
        appfunctions.py
        __init__.py

To import functions in main.py into appfunctions.py (import from parent directory), we can use the following syntax:

from ..main import *

Due to how relative imports are resolved in Python, executing appfunctions.py in the normal way (i.e. running python appfunctions.py) will fail with the following error:

ImportError: attempted relative import with no known parent package

This happens because Python will assume that appfunctions.py is at the top of the module hierarchy when executed directly. To provide Python with the correct context for appfunctions.py, we must call it using the -m (module) syntax. Run the following command from the parent directory of project:

python -m project.app.appfunctions

To import functions in libfunctions.py into appfunctions.py (import from sibling directory), we can use the following syntax in appfunctions.py:

from ..lib.libfunctions import *

As with imports from parent directories, we must use -m syntax to execute appfunctions.py, or execution will fail due to an ImportError.

Importing From Parent or Sibling Directories by Changing PYTHONPATH

As we’ve seen, package relative imports can be quite brittle and will prevent us from executing Python scripts in the normal way. An alternative method for importing scripts from parent or sibling directories is to add the directory to the system path before importing it. This avoids the issues with relative imports.

For example, to import main.py into appfunctions.py (import from parent directory), we can write the following:

import os, sys

sys.path.insert(1, "/".join(os.path.realpath(__file__).split("/")[0:-2]))

import main

Here we’re creating the path to main.py by taking the full path of appfunctions.py and slicing the last two segments ("app/appfunctions.py") from it. We insert it into the system path at index 1 to ensure that it resolves after the main script but before anything else. Once this is done, we can import main.py or any other files in project using their names, as we would with installed modules.

To import functions from libfunctions.py in appfunctions.py (import from sibling directory), we can write the following:

import os, sys

sys.path.insert(1, "/".join(os.path.realpath(__file__).split("/")[0:-2]) + "/lib")

import libfunctions

To import both, we can add main.py’s directory to the path and import libfunctions.py as if it were in a child directory.

import os, sys

sys.path.insert(1, "/".join(os.path.realpath(__file__).split("/")[0:-2]))

import main
from lib.libfunctions import *

Altering the system path is a convenient hack for importing files in this way, but can cause problems if we have files with the same names in different directories.