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GeezerVison is showing github.com — Allow keyword errors for UTF-8 decoders by jw9829 · Pull Request #16447 · python/typeshed

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@jw9829

@jw9829 jw9829 commented Sep 27, 2026 •
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Fixes #16441.

The UTF-8 decoder returned by codecs.lookup() accepts errors= as a keyword. Other codecs keep a positional-only signature because some reject keyword arguments.

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jw9829 added 2 commits September 26, 2026 22:53
@jw9829
[codecs] Allow keyword errors for decoders
fda9cbc
@jw9829
[codecs] Add decoder keyword regression
62b97fc
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JelleZijlstra
JelleZijlstra reviewed Sep 27, 2026
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Comment thread stdlib/codecs.pyi Outdated
@type_check_only
class _Decoder(Protocol):
def __call__(self, input: ReadableBuffer, errors: str = ..., /) -> tuple[str, int]: ... # signature of Codec().decode
def __call__(self, input: ReadableBuffer, /, errors: str = ...) -> tuple[str, int]: ... # signature of Codec().decode

@JelleZijlstra JelleZijlstra Sep 27, 2026

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This is not correct for all codecs:

>>> codecs.lookup("ascii").decode(b"abc", errors="replace")
Traceback (most recent call last):
  File "<python-input-3>", line 1, in <module>
    codecs.lookup("ascii").decode(b"abc", errors="replace")
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: _codecs.ascii_decode() takes no keyword arguments

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@jw9829
[codecs] Limit keyword errors to UTF-8
fce814f
@jw9829 jw9829 changed the title Allow keyword errors for codec decoders Allow keyword errors for UTF-8 decoders Sep 27, 2026
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[pre-commit.ci] auto fixes from pre-commit.com hooks
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github-actions Bot commented Sep 27, 2026

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According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

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JelleZijlstra
JelleZijlstra reviewed Sep 28, 2026
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Comment thread stdlib/codecs.pyi Resolved

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@JelleZijlstra JelleZijlstra mentioned this pull request Nov 4, 2026
Allow errors keyword argument in codecs _Encoder, _Decoder, and stream protocols #16697
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false alarm on decode call

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@jw9829 @JelleZijlstra
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