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bpo-36411: Python 3 f.tell() gets out of sync with file pointer in binary append+read mode #13717

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bpo-36411: Python 3 f.tell() gets out of sync with file pointer in binary append+read mode #13717

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websurfer5
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@websurfer5 websurfer5 commented Jun 1, 2019 •
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Implement buffered tell() as a wrapper for buffered seek(0, io.SEEK_CUR) to fix a problem with the internally maintained file position getting out of sync with the kernel when using read/write append mode. The fix applies to both binary and text files.

https://bugs.python.org/issue36411

@websurfer5
bpo-36411: explicitly specify character encoding when opening the
10d6183 
text file for read/write append. This is required for Windows systems.
@csabella csabella requested a review from benjaminp June 1, 2019 11:03
@brettcannon brettcannon added the type-bug An unexpected behavior, bug, or error label Jun 3, 2019
ZackerySpytz
ZackerySpytz reviewed Jul 13, 2019
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benjaminp
benjaminp requested changes Sep 11, 2019
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Won't this break calling tell() on buffered streams wrapping raw io that supports tell() but not seek()?

Modules/_io/bufferedio.c
*/

CHECK_INITIALIZED(self)
PyObject *z_obj = PyLong_FromLong(0);
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This looks like it leaks a reference to z_obj.

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A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

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Wouldn't it be possible to use the old buffered_tell() code if the stream doesn't support seek()? As far as I know, the bug only happens after seeking, so it ought to be fine to fall back to the old approach when seeking isn't possible, I would imagine.

@pewscorner pewscorner mannequin mentioned this pull request Apr 10, 2022
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@auvipy auvipy auvipy approved these changes

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@websurfer5 @bedevere-bot @pewscorner @benjaminp @auvipy @ZackerySpytz @brettcannon @the-knights-who-say-ni @ezio-melotti