bpo-36411: Python 3 f.tell() gets out of sync with file pointer in binary append+read mode by websurfer5 · Pull Request #13717 · python/cpython (original) (raw)

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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

text file for read/write append. This is required for Windows systems.

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Won't this break calling tell() on buffered streams wrapping raw io that supports tell() but not seek()?

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This looks like it leaks a reference to z_obj.

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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.