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Failed BytesIO reinitialization mutates the stream's position and contents #157048
Description
Bug report
Bug description:
Python 3.16.0a0 (heads/main:09117bc, Sep 6 2026, 15:04:05) [Clang 21.0.0 (clang-2100.1.1.101)] on darwin
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>>> import io
...
... stream = io.BytesIO(b"abcd")
... stream.seek(2)
... view = stream.getbuffer()
... try:
... stream.__init__(b"replacement")
... except BufferError:
... pass
... print(stream.tell(), stream.getvalue(), bytes(view))
... # 0 b'' b'abcd'
... view.release()
...
0 b'' b'abcd'This is happening because the implementation of BytesIO.__init__ resets state before checking for the BufferError:
Lines 1129 to 1137 in 09117bc
CPython versions tested on:
3.16, CPython main branch
Operating systems tested on:
macOS
Linked PRs
- gh-157048: check for buffer errors before mutating in BytesIO.__init__ #157049
- [3.14] gh-157048: check for buffer errors before mutating in BytesIO.__init__ (GH-157049) #157068
- [3.15] gh-157048: check for buffer errors before mutating in BytesIO.__init__ (GH-157049) #157069
- [3.13] gh-157048: check for buffer errors before mutating in BytesIO.__init__ (GH-157049) #157070
Activity
gh-157048: check for buffer errors before mutating in BytesIO.__init__ (
[3.14] gh-157048: check for buffer errors before mutating in BytesIO.…
[3.13] gh-157048: check for buffer errors before mutating in BytesIO.…
pythongh-157048: check for buffer errors before mutating in BytesIO._…
[3.15] gh-157048: check for buffer errors before mutating in BytesIO.…