How to use relative paths in Python

This guide shows you how to write a Python script whose file paths keep working when you move it between your own computer and LINCOMM (Linux Community Servers). Python makes this clean: you anchor paths to the script's own location, and then it runs correctly from anywhere. For the concept behind this, see Understanding relative paths.

Prerequisites

• A Python script and its data files, kept together in one project folder.
• Python 3, which is what LINCOMM provides.

Steps

1. Lay out your project so the data sits in a known place relative to the script:

   myproject/
     analysis.py
     data/
       transactions.csv

2. At the top of analysis.py, anchor to the script's own folder using pathlib. The built-in name __file__ is the path to the running script, and .parent is the folder it lives in:

   from pathlib import Path
   
   here = Path(__file__).parent

   HERE now points to the folder containing analysis.py, on any computer.

3. Build every data path from HERE, then read as normal. The / operator joins path parts safely on every operating system:

   import pandas as pd
   
   data_file = HERE / "data" / "transactions.csv"
   df = pd.read_csv(data_file)

   To reach a file in the parent folder, use HERE.parent, which is one level up.

4. Run the script:

   python analysis.py

Verify it worked

Copy the whole myproject folder to LINCOMM, then run the script from a different folder than the project itself:

cd /mnt/aae/users/jdoe
python myproject/analysis.py

It should find transactions.csv and run without any path edits, even though you launched it from outside the project folder.

If something went wrong

• FileNotFoundError: Check that the data folder was copied alongside the script, and that the names passed to Path match the real folder and file names exactly (Linux is case-sensitive).
• Worked when run from inside the folder but not outside: You may be using a bare path like "data/transactions.csv" instead of anchoring to HERE. Build the path from HERE as shown in step 3.

Download sample Python files