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> Akira, your patch does this:
>
> - self._writetranslate = newline != ''
> - self._writenl = newline or os.linesep
> + self._writetranslate = newline in (None, '\r', '\r\n')
> + self._writenl = newline if newline is not None else os.linesep
>
> Any reason you made the second change? Why change the value assigned
> to _writenl for newline='\n' when you don't want to actually change
> the behavior for those cases? Just so you can double-check at write
> time that _writetranslate is never set unless _writenl is '\r',
> \r\n', or os.linesep?
If newline='\n' then writenl is '\n' with and without the patch.
If newline='\n' then write('\n\r') writes '\n\r' with and without the
patch.
If newline='\n' then writetranslate=False (with the patch). It does not
change the result for newline='\n' as it is documented now [1]:
 [newline] can be None, '', '\n', '\r', and '\r\n'.
 ...
 If newline is any of the other legal values [namely '\r', '\n',
 '\r\n'], any '\n' characters written are translated to the given
 string.
[...] are added by me for clarity.
[1] https://docs.python.org/3.4/library/io.html#io.TextIOWrapper
writetranslate=False so that if newline='0円' then write('0円\n') would
write '0円\n' i.e., embed '\n' are not corrupted if newline='0円'. That is
why it is the "no translation" patch:
+ When writing output to the stream:
+
+ - if newline is None, any '\n' characters written are translated to
+ the system default line separator, os.linesep
+ - if newline is '\r' or '\r\n', any '\n' characters written are
+ translated to the given string
+ - no translation takes place for any other newline value [any string].