[Python-Dev] eval and triple quoted strings

Guido van Rossum guido at python.org
Tue Jun 18 01:52:21 CEST 2013

On Mon, Jun 17, 2013 at 4:40 PM, Benjamin Peterson <benjamin at python.org> wrote:
> 2013/6/17 Greg Ewing <greg.ewing at canterbury.ac.nz>:
>> Guido van Rossum wrote:
>>> No. Executing a file containing those exact characters produces a
>>> string containing only '\n' and exec/eval is meant to behave the same
>>> way. The string may not have originated from a file, so the universal
>>> newlines behavior of the io module is irrelevant here -- the parser
>>> must implement its own equivalent processing, and it does.
>> I'm still not convinced that this is necessary or desirable
>> behaviour. I can understand the parser doing this as a
>> workaround before we had universal newlines, but now that
>> we do, I'd expect any Python string to already have newlines
>> converted to their canonical representation, and that any CRs
>> it contains are meant to be there. The parser shouldn't need
>> to do newline translation a second time.
> It used to be that way until 2.7. People like to do things like
>     with open("myfile.py", "rb") as fp:
>         exec fp.read() in ns
> which used to fail with CRLF newlines because binary mode doesn't have
> them. I think this is actually the correct way to execute Python
> sources because the parser then handles the somewhat complicated
> process of decoding Python source for you.

What exactly does the parser handles better than the io module? Is it
just the coding cookies? I suppose that works as long as the file is
encoded using as ASCII superset like the Latin-N variants or UTF-8. It
would fail pretty badly if it was UTF-16 (and yes, that's an
abominable encoding for other reasons :-).
--Guido van Rossum (python.org/~guido)

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