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fix: escape % in class-variable comments so argparse help formatting does not crash (#183) #185

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Merged
martinjm97 merged 1 commit into from
Aug 29, 2026
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fix: escape % in class-variable comments so argparse help formatting does not crash (#183) #185

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3 changes: 2 additions & 1 deletion src/tap/tap.py
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Original file line number Diff line number Diff line change
Expand Up @@ -182,7 +182,8 @@ def _add_argument(self, *name_or_flags, **kwargs) -> None:

# Description
if variable in self.class_variables and (comment := self.class_variables[variable]["comment"]):
kwargs["help"] += " " + comment
# Escape "%" so a literal percent in a comment doesn't crash argparse's "%"-formatting of the help string.
kwargs["help"] += " " + comment.replace("%", "%%")

# Set other kwargs where not provided
if variable in self._annotations:
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10 changes: 10 additions & 0 deletions tests/test_integration.py
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@martinjm97 martinjm97 Jul 11, 2026 •
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This test would benefit from a full string match to ensure the parse is actually "The % chance this will break" and not mangled.

Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,16 @@ class ParseTwiceTap(Tap):
with self.assertRaises(ValueError):
ParseTwiceTap().parse_args(["--a", "6"]).parse_args(["--a", "7"])

def test_comment_with_percent(self) -> None:
# A '%' in a class-variable comment must not crash argparse's '%' formatting of the help string (#183).
class PercentCommentTap(Tap):
percent: int = 100 # The % chance this will break

# On Python <3.14 the crash surfaces when argparse %-formats the help; on 3.14 it
# surfaces eagerly during construction. Either way this must not raise.
help_text = PercentCommentTap().format_help()
self.assertIn("chance this will break", help_text)


class RequiredClassVariableTests(TestCase):
def setUp(self) -> None:
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