gh-155389: Return bytes from _pyio.BytesIO.peek() - #155390
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serhiy-storchaka merged 2 commits intoAug 16, 2026
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peek() returned a slice of the internal bytearray, where read() converts with take_bytes(). It also did not coerce its size through __index__ and did not hold the lock while slicing, both of which read() and the C implementation do.
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cmaloney
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Aug 8, 2026
| size = size_index() | ||
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| with self._lock: | ||
| if size < 1: |
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I don't think the size piece here needs to be in the lock
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Done, thanks. Only the slicing is under the lock now.
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It's better to add a test to check if |
The size normalisation touches no shared state, so it does not need the lock.
aisk
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Aug 9, 2026
cmaloney
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Aug 15, 2026
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for news, falls under the existing news add in: 72cad14. This is just refining behavior. |
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_pyio.BytesIO.peek()returned a slice of the internalbytearray, so it gave abytearraywhere the C version and the docs saybytes. It also did not accept an__index__-able size, and did not take the lock while slicing.It now does what
read()does: coerce the size, take the lock, convert withtake_bytes().test_peekonly usedassertEqual, andbytearray(b'1') == b'1', so it passed either way. It now checks the type and an__index__size, and fails without the change.BytesIO.peek()is new in 3.16, so there is no NEWS entry._pyio.BytesIO.peek()returns bytearray instead of bytes #155389