On 9/26/07, Dino Viehland <[EMAIL PROTECTED]> wrote:
> We ran into an interesting user-reported issue w/ IronPython and the way
> Python writes to files and I thought I'd get python-dev's opinion.
>
> When writing a string in text mode that contains \r\n we both write \r\r\n
> because the default write mode is to replace \n with \r\n. This works great
> as long as you stay within an entirely Python world. Because Python uses \n
> for everything internally you'll never end up writing out a \r\n that gets
> transformed into a \r\r\n. But when interoperating with other native code
> (or .NET code in our case) it's fairly easy to be exposed to a string which
> contains \r\n. Ultimately we see odd behavior when round tripping the
> contents of a multi-line text box through a file.
>
> So today users have to be aware of the fact that Python internally always
> uses \n. They also need to be aware of any APIs that they call that might
> return a string with an embedded \r\n inside of them and transform the string
> back into the Python version.
>
> It could be argued that there's little value in doing the simple
> transformation from \r\n -> \r\r\n. Ultimately that creates a file that has
> line endings which aren't good on any platform. On the other hand it could
> also be argued that Python defines new-lines as \n and there should be no
> deviation from that. And doing so could be considered a slippery slope,
> first file deals with it, and next the standard libraries, etc... Finally
> this might break some apps and if we changed IronPython to behave differently
> we could introduce incompatibilities which we don't want.
>
> So I'm curious: Is there a reason this behavior is useful that I'm missing?
No, it is simply the way Microsoft's C stdio library works. :-(
A simple workaround would be to apply s.replace('\r', '') before
writing anything of course.
> Would there be a possibility (or objections to) making \r\n be untransformed
> in the Py3k timeframe? Or should we just tell our users to open files in
> binary mode? :)
Py3k supports a number of different ways of working with newlines for
text files, but not (yet) one that leaves \r\n alone while translating
a lone \n into \r\n. It may not be too late to change that though.
--
--Guido van Rossum (home page: http://www.python.org/~guido/)
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