Python: import symbolic link of a folder

Question

I have a folder A which contains some Python files and __init__.py.

If I copy the whole folder A into some other folder B and create there a file with "import A", it works. But now I remove the folder and move in a symbolic link to the original folder. Now it doesn't work, saying "No module named foo". Does anyone know how to use symlink for importing?

Weekly

Answer 1

Python doesn't check if your file is a symlink or not! Your problem lies probably in renaming the modules or not having them in your search-path!

If ModuleA becomes ModuleB and you try to import ModuleA it can't find it, because it doesn't exist.

If you moved ModuleA into another directory and you generate a symlink with another name, which represents a new directory, this new directory must be the common parent directory of your script and your module, or the symlink directory must be in the search path.

BTW it's not clear if you mean module or package. The directory containing the __init__.py file becomes a package of all files with the extension .py (= modules) residing therein.

Example

DIRA
  + __init__.py    <-- makes DIRA to package DIRA
  + moduleA.py     <-- module DIRA.moduleA

Moving and symlink

/otherplace/DIRA  <-+
                    |  points to DIRA
mylibraries/SYMA  --+  symbolic link

If SYMA has the same name as DIRA and your script is in the directory SYMA then it should just work fine. If not, then you have to:

import sys
sys.path.append('/path/to/your/package/root')

If you want to import a module from your package SYMA you must:

import SYMA.ModuleA

A simple:

import SYMA

will import the packagename, but not the modules in the package into your namespace!

Unsound

I think this answer may only apply when running python under Windows. It seems that on my mac, python DOES check if the file is a symlink. (https://mcmap.net/q/137241/-where-is-python-39-s-sys-path-initialized-from) – Hague

Answer 2

This kind of behavior can happen if your symbolic links are not set up right. For example, if you created them using relative file paths. In this case the symlinks would be created without error but would not point anywhere meaningful.

If this could be the cause of the error, use the full path to create the links and check that they are correct by lsing the link and observing the expected directory contents.

Bantamweight

I just falled into this, thanks! – Osteoclasis

To flesh out this answer, when making your symlinks be sure you are using ln -s "$PWD/path/to/fileordir" "$PWD/path/to/symlink" – Contraption