馃悰 fix: expand argparse format specifiers in help text - #355
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Help strings such as "count (default: %(default)s)" and descriptions with "%(prog)s" rendered with the literal specifier, followed by the extension's own (default: "3") suffix. A help string starting with "Default: 3" got the same duplicate because the existing-default check was case-sensitive and demanded a space after the word. Reimplement argparse's _expand_help on the public Action attributes, apply the %(prog)s substitution from _format_text to descriptions and epilogs of the root, groups and sub-commands, and detect an existing default mention with a case-insensitive word match.
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Help strings written for argparse use its format specifiers, so
help="count (default: %(default)s)"anddescription="%(prog)s does things"are common. The directive handed those strings to docutils untouched. The page showed the literal%(default)sand%(prog)s, followed by a second(default: "3")that the extension appends on its own. A help string starting withDefault: 3got the same duplicate, since the check for an existing default mention was case-sensitive and required a space after the word.Help now goes through the same expansion
argparse.HelpFormatter._expand_helpperforms, reimplemented on the publicActionattributes so it does not depend on which formatter class the parser ended up with. It expands%(prog)s,%(default)s,%(choices)sjoined with commas,%(type)sas the callable name, and%%. Descriptions and epilogs of the root, of argument groups, and of sub-commands get the%(prog)ssubstitution argparse applies in_format_text, each with its own parser's prog. 馃ЗThe generated default suffix is skipped whenever the expanded help contains the word
default, in any case and with any punctuation after it. Pages whose help already spelled out the default lose the duplicate.