Inside a Python Package / Module - how to define a relative path to a file?

Question

I am working on a Python Toolbox running on Windows, that needs to know several paths:

Folders, e.g. /path/to/output, /path/to/calc/, /fixed/path/to/server
Programs, e.g. /path/to/program.exe

Some of these paths are fixed and could be hard coded. Some of them change depending on the user.

At the moment I solve that problem using a config file config.param. This file has to be created by each user.

The reason why I chose such a config file is, that inexperienced users can simply copy this file from someone else and change the content according to their system.

The directory looks like this

Toolbox
 |
 +-- config.param
 |
 +-- package
 |    |
 |    +-- __init__.py
 |    |
 |    +-- path_and_names.py
 |
 +-- example
      |
      +-- example.py
      |
      + example_sub
         |
         +-- example_sub.py

For internal use of all path-variables, I use a class called PathAndNames. The problem is now reduced to: This class PathAndNames needs to know the location of the file config.param. Since both are part of the Python package with a fixed relative path, I solved that by

class PathAndNames:
    PATH_TO_CONFIG = os.path.normpath("../config.param")

Problem:

Since this is a Toolbox the user should be able to use it from /where/he/likes, e.g. where his Calculation-Folder is located. He will need to create an instance of PathAndNames, which then should know all correct paths.

The problem is, that ../config.param now refers to /where/he/likes/../config.param and not the correct path inside the Toolbox.

Example:

The user is at the moment forced to write his code in a subfolder of the Toolbox, e.g. like example.py in the subfolder Toolbox/example/. If the folder is located not in a direct subfolder of Toolbox, e.g. like example_sub.py in the subsubfolder Toolbox/example/example_sub, then the Toolbox won't work. In this example the location of ../config.param that PathAndNames knows, would be Toolbox/example/config.param.

Is there a way to define a relative path inside a Python package / module?
Are there other possible ways to solve the path problem, in a way that inexperienced users can understand what they should do?

Any ideas are appreciated.

scnerd · Accepted Answer · 2017-08-28 13:46:46Z

3

The __file__ attribute will get the absolute file path to the module in which you call it (rather than the working directory of whichever file loads it). This allows you to define two files, say config.param and config.py, then in config.py you can put a line like the following:

import os
__here__ = os.path.join(*list(os.path.split(os.path.dirname(__file__)))[:-1])
PATH_TO_CONFIG = os.path.join(__here__, 'config.param')

From the user script, then you can get the file path as

from my_module.config import PATH_TO_CONFIG

answered Aug 28, 2017 at 13:46

scnerd

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2 Comments

P. Siehr Over a year ago

I am feeling quite dumb right now. Especially since I postponed this problem for several weeks ;) Thanks a lot for your answer. `

P. Siehr Over a year ago

Small addition: If /path/to/__file__ contains symbolic links os.path.dirname() will return an empty string. Using os.path.realpath() solves this.

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