[Python-3000] Proposed new language for newline parameter to TextIOBase

[Brett Cannon]

On 8/14/07, Guido van Rossum <guido at python.org> wrote:
> I thought some more about the universal newlines situation, and I
> think I can handle all the use cases with a single 'newline'
> parameter. The use cases are:
>
> (A) input use cases:
>
> (1) newline=None: input with default universal newlines mode; lines
> may end in \r, \n, or \r\n, and these are translated to \n.
>
> (2) newline='': input with untranslated universal newlines mode; lines
> may end in \r, \n, or \r\n, and these are returned untranslated.
>
> (3) newline='\r', newline='\n', newline='\r\n': input lines must end
> with the given character(s), and these are translated to \n.
>
> (B) output use cases:
>
> (1) newline=None: every \n written is translated to os.linesep.
>
> (2) newline='': no translation takes place.
>
> (3) newline='\r', newline='\n', newline='\r\n': every \n written is
> translated to the value of newline.
>

I like the options, but I would swap the meaning of None and the empty
string.  My reasoning for this is that for option 3 it says to me
"here is a string representing EOL, and make it \n".  So I would think
of the empty string as, "I don't know what EOL is, but I want it
translated to \n".  Then None means, "I don't want any translation
done" by the fact that the argument is not a string.  In other words,
the existence of a string argument means you want EOL translated to
\n, and the specific value of 'newline' specifying how to determine
what EOL is.

-Brett