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GH-142950: Process format specifiers before colourization in argparse help #142960

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Merged
savannahostrowski merged 8 commits into from
Jan 7, 2026
Merged

GH-142950: Process format specifiers before colourization in argparse help #142960

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b3deacc
Format before colourization
savannahostrowski Dec 18, 2025
987af8b
Clean up
savannahostrowski Dec 18, 2025
2e73cd5
Comments
savannahostrowski Dec 18, 2025
8fc4cd2
📜🤖 Added by blurb_it.
blurb-it[bot] Dec 18, 2025
62ceb27
Lint
savannahostrowski Dec 18, 2025
e599afa
Address additional cases
savannahostrowski Jan 4, 2026
95919d9
Merge branch 'main' into argparse-format-specifier
savannahostrowski Jan 4, 2026
4d13744
Merge branch 'main' into argparse-format-specifier
savannahostrowski Jan 7, 2026
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Address additional cases
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@savannahostrowski
savannahostrowski committed Jan 4, 2026
commit e599afa05f0f92637bb451f7079c7e96c99ae25b
38 changes: 25 additions & 13 deletions Lib/argparse.py
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Original file line number Diff line number Diff line change
Expand Up @@ -691,26 +691,38 @@ def _expand_help(self, action):

t = self._theme

result = help_string % params
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if not t.reset:
return help_string % params
return result

# Match format specifiers like: %s, %d, %(key)s, etc.
fmt_spec = r'''
%
(?:
% # %% escape
|
(?:\((?P<key>[^)]*)\))? # key
[-#0\ +]* # flags
(?:\*|\d+)? # width
(?:\.(?:\*|\d+))? # precision
[hlL]? # length modifier
[diouxXeEfFgGcrsa] # conversion type
)
'''
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# Format first to preserve types for specifiers, like %x that require int.
def colorize(match):
spec, name = match.group(0, 1)
spec, key = match.group(0, 'key')
if spec == '%%':
return '%'
if name in params:
formatted = spec % {name: params[name]}
if key is not None:
# %(key)... - format and colorize
formatted = spec % {key: params[key]}
return f'{t.interpolated_value}{formatted}{t.reset}'
return spec
# bare %s etc. - format with full params dict, no colorization
return spec % params

# Match %% or %(name)... format specifiers
result = _re.sub(r'%%|%\((\w+)\)[^a-z]*[a-z]', colorize,
help_string, flags=_re.IGNORECASE)

if '%' in result:
raise ValueError(f"invalid format specifier in: {help_string!r}")
return result
return _re.sub(fmt_spec, colorize, help_string, flags=_re.VERBOSE)

def _iter_indented_subactions(self, action):
try:
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18 changes: 17 additions & 1 deletion Lib/test/test_argparse.py
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Expand Up @@ -7667,17 +7667,33 @@ def test_help_with_format_specifiers(self):
# GH-142950: format specifiers like %x should work with color=True
parser = argparse.ArgumentParser(prog='PROG', color=True)
parser.add_argument('--hex', type=int, default=255,
help='hex: %(default)x')
help='hex: %(default)x, alt: %(default)#x')
parser.add_argument('--zero', type=int, default=7,
help='zero: %(default)05d')
parser.add_argument('--str', default='test',
help='str: %(default)s')
parser.add_argument('--pct', type=int, default=50,
help='pct: %(default)d%%')
parser.add_argument('--literal', help='literal: 100%%')
parser.add_argument('--prog', help='prog: %(prog)s')
parser.add_argument('--type', type=int, help='type: %(type)s')
parser.add_argument('--choices', choices=['a', 'b'],
help='choices: %(choices)s')

help_text = parser.format_help()

interp = self.theme.interpolated_value
reset = self.theme.reset

self.assertIn(f'hex: {interp}ff{reset}', help_text)
self.assertIn(f'alt: {interp}0xff{reset}', help_text)
self.assertIn(f'zero: {interp}00007{reset}', help_text)
self.assertIn(f'str: {interp}test{reset}', help_text)
self.assertIn(f'pct: {interp}50{reset}%', help_text)
self.assertIn('literal: 100%', help_text)
self.assertIn(f'prog: {interp}PROG{reset}', help_text)
self.assertIn(f'type: {interp}int{reset}', help_text)
self.assertIn(f'choices: {interp}a, b{reset}', help_text)

def test_print_help_uses_target_file_for_color_decision(self):
parser = argparse.ArgumentParser(prog='PROG', color=True)
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