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gh-86427: Determine the stdio encoding for every standard stream on Windows - #155416
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serhiy-storchaka merged 3 commits intoSep 18, 2026
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August 9, 2026 10:50
It was the ANSI code page instead of the encoding of the device the stream is connected to, as in 3.7. The stdio encoding is now left undefined in this mode and determined for every standard stream.
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vstinner
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LGTM. This change is a simple fix.
I saw other more complicated options being discussed like having one encoding member per stream in PyConfig. It would work since it sounds more complicated. So yeah, I like this approach of delegating the encoding choice to create_stdio() using _Py_device_encoding(fd).
Also, test_cmd_line checks properly that two sys streams can have different encodings.
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| /* gh-86427: it is determined for each stream. */ |
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Can you mention that create_stdio() calls _Py_device_encoding() to get the device encoding in this case?
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Thank you for your review. This change is not backportable, because it can crash a program that did not expect |
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PyConfig.stdio_encodingis now left undefined in the legacy Windows stdio mode, and the encoding of every standard stream is determined from the device it is connected to.sys.stdin.encodingandsys.stdout.encodingcan therefore differ, and a redirected stream uses the locale encoding.This makes the member optional, which @vstinner objected to in the issue. #155415 is the minimal fix which is suitable for backporting.