I backported and adapted most Python 3 fixes related to the Windows binary mode for stdout/stderr used when Python is started with the -u command line option. See attached binary.patch.

My change to file.write() looks wrong because the function returns None and does not loop until all bytes are written.

By the way, string_write() doesn't check if fwrite(n) wrote less than n bytes or failed with an error.

See also the issue #21090 which improves error handling in the file object.