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GeezerVison is showing github.com — gh-161730: Fix the mode in the `compression.zstd.open()` invalid mode error by andresdelfino · Pull Request #161731 · python/cpython

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@andresdelfino

@andresdelfino andresdelfino commented Nov 10, 2026 •
edited by bedevere-app Bot
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compression.zstd.open() removed 't' from the mode before checking for the invalid 't' and 'b' combination, and formatted the error message with the modified string. For 'rtb' the message was Invalid mode: 'rb', which names a valid mode the caller didn't pass. This moves the mode.replace('t', '') call after the check, so the message shows the mode as passed (Invalid mode: 'rtb'), like gzip.open(), bz2.open() and lzma.open().

🤖 Generated with Claude Code

  • Issue: compression.zstd.open() names the wrong mode in its invalid mode error #161730

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@andresdelfino @claude
pythongh-161730: Fix the mode in the compression.zstd.open() invalid …
16d968c 
…mode error

compression.zstd.open() removed 't' from the mode before checking for
the invalid 't' and 'b' combination, so the error message named the
modified mode (e.g. "Invalid mode: 'rb'" for 'rtb'), which is a valid
mode the caller didn't pass.  Check before removing 't', matching
gzip.open(), bz2.open() and lzma.open().

Co-Authored-By: Claude Opus 5.5 <[email protected]>
@andresdelfino
andresdelfino requested review from AA-Turner and emmatyping as code owners November 10, 2026 02:37
@bedevere-app bedevere-app Bot mentioned this pull request Nov 10, 2026
compression.zstd.open() names the wrong mode in its invalid mode error #161730
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@bedevere-app bedevere-app Bot added the awaiting review label Nov 10, 2026
@aisk

aisk commented Nov 10, 2026 •
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The fix looks good to me, but I think it would be better to update the existing test to prevent regressions, perhaps by using assertRaisesRegex on this line:

cpython/Lib/test/test_zstd.py

Lines 2715 to 2716 in e891a91

with self.assertRaises(ValueError):
open(TESTFN, "rbt")

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@andresdelfino

andresdelfino commented Nov 10, 2026

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Sure, will do.
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@andresdelfino @claude
Check the error message in the zstd invalid mode test
3738161 
Co-Authored-By: Claude Opus 5.5 <[email protected]>
aisk
aisk approved these changes Nov 10, 2026
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@bedevere-app bedevere-app Bot added awaiting core review and removed awaiting review labels Nov 10, 2026
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@aisk aisk aisk approved these changes
@AA-Turner AA-Turner Awaiting requested review from AA-Turner AA-Turner is a code owner
@emmatyping emmatyping Awaiting requested review from emmatyping emmatyping is a code owner

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@andresdelfino @aisk
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