从父目录导入 function

Question

I have a directory which contains a bunch of function and another folder which contains my main project which I would like to be able to run from the terminal: kf_sine_demo.py .

When I run line by line the code from VS-Code (using Shift + Enter ), everything works fine. In particular I can import the functions for further use:

from EKFUKF_Py import lti_disc, kf_predict, kf_update, rts_smooth

However, when I run the file from the terminal:

python kf_sine_demo.py

I get the following error:

Traceback (most recent call last):
  File "EKFUKF_Py/demo/kf_sine_demo/kf_sine_demo.py", line 16, in <module>
    from EKFUKF_Py import lti_disc, kf_predict, kf_update, rts_smooth
ModuleNotFoundError: No module named 'EKFUKF_Py'

I see solutions which include specifying the full path. I have strong preference for relative imports.

---

UPDATE:

This solution has been most useful to me: https://stackoverflow.com/a/37193862/4576194 .

• Run python -m EKFUKF_Py.demo.kf_sine_demo.kf_sine_demo form the parent directory of EKFUKF_Py

But, that's not quite what I want. I want to be able to run python kf_sine_demo.py from kf_sine_demo directory and I want it to know that the functions it needs to import are located 2 levels up.

Answer 1

You have to understand how python path works. This is a list of directories where python looks for the modules you try to import, you can display it uing the sys.path command. There are a bunch of directories that python automatically add to, like path\to\your_python_install\lib , and python also add the working directory when you run a script.

This means that when you do:

python kf_sine_demo.py

The parent directory of this file (kf_sine_demo) is added to the path, but the EKFUKF_Py is not. Thus python can not find the modules in it.

From here, two solutions. Either you manually add this directory (which I find a little ugly, but it works):

sys.path.append("path/to/EKFUKF_Py")

Or you ensure to always run your files from the main directory, through a main.py file, for example. from there, you will be able to call every submodule in this directory.

More here: https://www.devdungeon.com/content/python-import-syspath-and-pythonpath-tutorial