gh-127296: Document that argparse count action starts from a non-zero default

[owenthcarey]

The 'count' action adds to whatever value is already in the namespace, so with default=3 a single -v gives 4, not 1. The docs don't say this, and the general description of default reads as if the default is only used when the argument is absent.

This adds one sentence to the 'count' entry saying that a non-zero default is the starting point for the count, as suggested in the issue.

Fixes #127296

• Issue: Argparse: "default" interacts incorrectly/non-intuitively with action="count" #127296

[read-the-docs-community]

Documentation build overview

📚 cpython-previews | 🛠️ Build #34409315 | 📁 Comparing 7cb271d against main (c8ea867)

  🔍 Preview build  

7 files changed · ± 7 modified

± Modified

• c-api/marshal.html
• library/argparse.html
• library/difflib.html
• library/sys.html
• whatsnew/3.15.html
• whatsnew/3.16.html
• whatsnew/changelog.html

[owenthcarey]

Thanks! Applied your suggestion.

[savannahostrowski]

Thank you!

[miss-islington-app]

Thanks @owenthcarey for the PR, and @savannahostrowski for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14, 3.15.
🐍🍒⛏🤖

[bedevere-app]

GH-156997 is a backport of this pull request to the 3.15 branch.

[bedevere-app]

GH-156998 is a backport of this pull request to the 3.14 branch.

[bedevere-app]

GH-156999 is a backport of this pull request to the 3.13 branch.