Add supporting code for Python Optional Arguments tutorial

[martin-martin]

Where to put new files:

• New files should go into a top-level subfolder, named after the article slug. For example: my-awesome-article

How to merge your changes:

1. Make sure the CI code style tests all pass (+ run the automatic code formatter if necessary).
2. Find an RP Team member on Slack and ask them to review & approve your PR.
3. Once the PR has one positive ("approved") review, GitHub lets you merge the PR.
4. 🎉

[Copilot]

Pull Request Overview

This PR adds supporting code files for a Real Python tutorial on Python optional arguments. The code demonstrates various patterns for working with optional parameters, including proper handling of mutable defaults and the use of *args and **kwargs.

• Provides working examples of safe optional parameter patterns using None defaults
• Demonstrates the mutable default bug and how to avoid it
• Includes examples of variadic functions using *args and **kwargs

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
README.md	Provides overview and instructions for the tutorial code
optional_params.py	Main examples showing proper optional parameter patterns
optional_params_mutable_default_bug.py	Demonstrates the dangerous mutable default antipattern
optional_params_unpacking_demo.py	Simple demonstration of argument unpacking with * operator

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[martin-martin]

@bzaczynski Copilot suggested to add quantity checks to the two functions that add to the shopping list via *args and **kwargs. I accepted, I think it makes sense, but decided not to make that same update in the tutorial text.

IMO the tutorial focuses the code on the essential aspect (how do *args and **kwargs work, with an example) so didactically it makes sense to keep those functions as small as possible. However, I don't mind readers getting the (slightly) more code with the extra check with their materials download and reason about the difference themselves. Seems like a helpful learning experience. LMK if you disagree :)

[bzaczynski]

🔧 Technical Recommendation

The name shopping_list may imply Python's list data structure, while we actually use the variable to store a Python dictionary. How about renaming this variable to shopping_items or item_quantities instead?

[bzaczynski]

@martin-martin This looks good to me. I'd only consider renaming some of the variables for better clarity, but it's not a big deal at all!