How to fix "ImportError: No module named ..." error in Python?

Question

What is the correct way to fix this ImportError error?

I have the following directory structure:

/home/bodacydo
/home/bodacydo/work
/home/bodacydo/work/project
/home/bodacydo/work/project/programs
/home/bodacydo/work/project/foo

And I am in the directory

/home/bodacydo/work/project

Now if I type

python ./programs/my_python_program.py

I instantly get

ImportError: No module named foo.tasks

The ./programs/my_python_program.py contains the following line:

from foo.tasks import my_function

I can't understand why python won't find ./foo/tasks.py - it's there.

If I do it from the Python shell, then it works:

python
>>> from foo.tasks import my_function

It only doesn't work if I call it via python ./programs/my_python_program.py script.

Answer 1

Python does not add the current directory to sys.path, but rather the directory that the script is in. Add /home/bodacydo/work/project to either sys.path or $PYTHONPATH.

• user1980175: So whats the point then of having init.py in the root folder? It seems to serve no purpose if you edit either sys.path or the pythonpath.
• Ignacio Vazquez-Abrams: @Editor: __init__.py only indicates that the directory should be treated as a package, when its parent is either in sys.path or is itself a package.
• SidJ: In addition check the permissions on the folder. That was the problem in my case.
• rodorgas: To add current dir to python path, use export PYTHONPATH=`pwd`
• maledr53: What worked for me was to add to $PYTHONPATH the parent directory of the project, in your case will be: /home/bodacydo/work ... see this answer

Answer 2

Do you have a file called __init__.py in the foo directory? If not then python won't recognise foo as a python package.

See the section on packages in the python tutorial for more information.

• bodacydo: Thanks and yes, I had __init__.py. The problem this time was with $PYTHONPATH. Ignacio's solution worked.
• panofish: The init.py files are required to make Python treat the directories as containing packages; this is done to prevent directories with a common name, such as string, from unintentionally hiding valid modules that occur later on the module search path. In the simplest case, init.py can just be an empty file
• Karl Knechtel: __init__.py has nothing to do with making absolute imports work, and has not been required to make relative imports work since 3.3.

Answer 3

A better fix than setting PYTHONPATH is to use python -m module.path

This will correctly set sys.path[0] and is a more reliable way to execute modules.

I have a quick writeup about this problem, as other answerers have mentioned the reason for this is python path/to/file.py puts path/to on the beginning of the PYTHONPATH (sys.path).

Answer 4

Here is a step-by-step solution:

1. Add a script called run.py in /home/bodacydo/work/project and edit it like this:

   import programs.my_python_program
   programs.my_python_program.main()
   

   (replace main() with your equivalent method in my_python_program.)

2. Go to /home/bodacydo/work/project
3. Run run.py

Explanation: Since python appends to PYTHONPATH the path of the script from which it runs, running run.py will append /home/bodacydo/work/project. And voilà, import foo.tasks will be found.

Answer 5

Example solution for adding the library to your PYTHONPATH.

1. Add the following line into your ~/.bashrc or just run it directly:

   export PYTHONPATH="$PYTHONPATH:$HOME/.python"
   

2. Then link your required library into your ~/.python folder, e.g.

   ln -s /home/user/work/project/foo ~/.python/
   

Answer 6

In my mind I have to consider that the foo folder is a stand-alone library. I might want to consider moving it to the Lib\site-packages folder within a python installation. I might want to consider adding a foo.pth file there.

I know it's a library since the ./programs/my_python_program.py contains the following line:

from foo.tasks import my_function

So it doesn't matter that ./programs is a sibling folder to ./foo. It's the fact that my_python_program.py is run as a script like this:

python ./programs/my_python_program.py

Answer 7

If you have this problem when using an instaled version, when using setup.py, make sure your module is included inside packages

setup(name='Your program',
 version='0.7.0',
 description='Your desccription',
 packages=['foo', 'foo.bar'], # add `foo.bar` here