fix: use absolute path for aco_tsp data file

[himanksingh2024-svg]

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• 🐛 Bug fix
• 🛠 Feature/enhancement

Problem: The aco_tsp example fails with FileNotFoundError when run from the repo root directory because the data file path is relative.
Fix: Used os.path.dirname(file) to make the path absolute, so it works regardless of where the script is run from.
Fixes the error: FileNotFoundError: No such file or directory: 'aco_tsp/data/kroA100.tsp'

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GSoC contributor checklist

Context & motivation

I found this bug while testing mesa-examples locally. When running the aco_tsp example from the repo root, it throws a FileNotFoundError because the data file path is relative to the working directory, not the script location. This is a real usability issue for anyone trying to run the examples.

What I learned

I learned that file paths in Python scripts should use os.path.dirname(file) to be robust regardless of where the script is run from. I also learned the Mesa contribution workflow including forking, branching, and PR process.

Learning repo

🔗 My learning repo: https://github.com/himanksingh2024-svg/GSoC-learning-space
🔗 Relevant model(s): N/A (bug fix PR)

Readiness checks

• This PR addresses an agreed-upon problem (linked issue or discussion with maintainer approval), or is a small/trivial fix
• I have read the contributing guide and deprecation policy
• I have performed a self-review
• Another GSoC contributor has reviewed this PR: @
• Tests pass locally
• Code is formatted

[ShreyasN707]

also can you improve the PR description following the PR requirements mentioned in : mesa/mesa#3536 (comment)

[ShreyasN707]

since app.py is already inside the aco_tsp directory, the joined path may not need the extra aco_tsp/ prefix. Using:

os.path.join(os.path.dirname(__file__), "data/kroA100.tsp")

would resolve directly to the data folder next to the script.

[himanksingh2024-svg]

Updated the fix based on @ShreyasN707's review. The path is correct as aco_tsp/data/kroA100.tsp relative to app.py since the data folder is inside the aco_tsp subdirectory.

[EwoutH]

Cool seeing a peer-review going! I wrote down a checklist, maybe it's useful!

[himanksingh2024-svg]

Self-review:

• ✅ Fix is minimal — only changes the file path, nothing else
• ✅ Tested locally — python examples/aco_tsp/app.py runs with no errors
• ✅ No dead code or unused imports added (os was already needed)
• ✅ No deprecated APIs used
• ✅ Simplest solution to the FileNotFoundError problem

[ShreyasN707]

@EwoutH I have checked this PR locally and works. This is the notes:

Is it correct and current?

• Uses current Mesa APIs (no deprecated features)
• Fixes the FileNotFoundError caused by the relative data path
• Example runs correctly from different working directories

Is the fix appropriate?

• Uses a robust path resolution (os.path.dirname(__file__))
• Change is minimal and does not affect model logic

Is it clean?

• No unnecessary code changes
• Clear and readable modification
• PR description explains the issue and fix
• Commits are clean and relevant