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 #34380293 | 📁 Comparing 8da8655 against main (c8ea867)

  🔍 Preview build  

1 file changed

± library/argparse.html

[savannahostrowski]

Suggested change

	Note, the *default* will be ``None`` unless explicitly set to *0*.
	If the default value is a non-zero number, the count starts from that
	number rather than from zero.
	Unless explicitly set, the *default* will be ``None``. If the default
	value is a non-zero number, the count starts from that number rather
	than from zero.

Minor tweak because I think the preceding sentence could also be worded better.