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gh-153967: handle invalid file object in argparse._print_message #153969

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gh-153967: handle invalid file object in argparse._print_message #153969

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fd8fc3a
Handle invalid file object when passed explicitly
ptim0626 Jul 18, 2026
259fa8e
Add tests for valid/invalid file with stdout/err as None
ptim0626 Jul 18, 2026
84bc110
Update assertRaise to use context-manager format
ptim0626 Jul 18, 2026
2f22610
Remove redundant tests
ptim0626 Jul 18, 2026
b25daae
Add NEWS entry
ptim0626 Jul 18, 2026
27787e9
Modify invalid file test to include falsy object
ptim0626 Jul 18, 2026
516ff20
Refactor to a flatter structure and silently pass with falsy message
ptim0626 Jul 18, 2026
d0af2f4
Fix docs parser issue
ptim0626 Jul 19, 2026
97c6b58
Fix missing file name in meth ref
ptim0626 Jul 19, 2026
7a5d2ec
Merge branch 'main' into argparse-invalid-file-error
ZeroIntensity Jul 19, 2026
a5a4d6d
Merge branch 'main' into argparse-invalid-file-error
chris-eibl Jul 19, 2026
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15 changes: 9 additions & 6 deletions Lib/argparse.py
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Original file line number Diff line number Diff line change
Expand Up @@ -86,6 +86,7 @@
]


import io as _io
import os as _os
import re as _re
import sys as _sys
Expand Down Expand Up @@ -2885,12 +2886,14 @@ def print_help(self, file=None):
self._print_message(help_text, file)

def _print_message(self, message, file=None):
if message:
file = file or _sys.stderr
try:
file.write(message)
except (AttributeError, OSError):
pass
if not message:
return
if file is None:
file = _sys.stderr
elif not isinstance(file, _io.IOBase):
raise ValueError(f"invalid file object {file}")
if file is not None:
file.write(message)
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def _get_theme(self, file=None):
# If self.color is False, _colorize is not imported
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9 changes: 9 additions & 0 deletions Lib/test/test_argparse.py
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Original file line number Diff line number Diff line change
Expand Up @@ -79,6 +79,15 @@ def test_skip_invalid_stdout(self):
func()
self.assertRegex(mocked_stderr.getvalue(), r'usage:')

def test_invalid_file_only(self):
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parser = argparse.ArgumentParser()
for func in (parser.print_usage, parser.print_help):
for invalid_f in ("invalid file", "", 0):
with (
self.subTest(func=func, invalid_f=invalid_f),
self.assertRaises(ValueError),
):
func(file=invalid_f)

class TestLazyImports(unittest.TestCase):
LAZY_IMPORTS = {
Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-07-18-16-05-38.gh-issue-153967.-OUNXe.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
:meth:`argparse.ArgumentParser.print_usage` and
:meth:`argparse.ArgumentParser.print_help` won't silently fail when an invalid
file object is specified. Patch by Timothy Poon.
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