Sync python-function with the updated tutorial

[realpython-bot]

Companion-code sync for the maintenance update of Defining Your Own Python Function.

• Update draft (source of truth for the article's current state): https://realpython.com/pbjt/blog/post/2393/change/
• Maintenance card: https://trello.com/c/pytD9oO0

What changed

python-function/mutable_argument.py — the mutable-default-argument example had drifted away from the tutorial. The folder defined add_product(item, inventory=[]) and called it with "apple" / "banana", but the article's "Using Mutable Default Values" section defines append_to(item, target=[]) and calls it with 1, 2, 3. add_product() appears nowhere in the tutorial, so a reader downloading the materials couldn't match the file to the text. The script now transcribes the article's block exactly, and its output ([1], [1, 2], [1, 2, 3]) matches the tutorial's output character for character.

What this cycle changed in the article, and why nothing else moved here

The update's code-family fix was the print(average.__doc__) output block, dedented for the Python 3.13+ docstring-whitespace stripping — that's a REPL output block with no twin in this folder (average.py carries the undocumented average(), and there is no docstring script). The rest of the cycle was prose: fourteen {% ref %} glossary links, the PEP 257 link repointed to peps.python.org, and a factual fix to the mutable-default wording. The dependencies pin moved from python==3.13 to python==3.14; this folder has no requirements.txt or constraints.txt (the examples are pure standard library), so there is nothing to re-pin — the repo root already targets py314.

How this was verified

• Fresh uv venv on the article's new pin, CPython 3.14.6 (python==3.14).
• Every one of the 17 scripts in python-function/ executed to completion with exit 0 under MPLBACKEND=Agg; mutable_argument.py's output was diffed against the article's pycon block.
• Repo gates at the version pinned in the root requirements.txt (ruff==0.14.1):
  • uvx ruff@0.14.1 format --check python-function → 17 files already formatted
  • uvx ruff@0.14.1 check python-function → All checks passed!

Needs a human merge.

🤖 Generated with Claude Code