[Python-Dev] What does a double coding cookie mean?

M.-A. Lemburg mal at egenix.com
Thu Mar 17 09:14:33 EDT 2016

On 17.03.2016 01:29, Guido van Rossum wrote:
> I've updated the PEP. Please review. I decided not to update the
> Unicode howto (the thing is too obscure). Serhiy, you're probably in a
> better position to fix the code looking for cookies to pick the first
> one if there are two on the same line (or do whatever you think should
> be done there).

Thanks, will do.

> Should we recommend that everyone use tokenize.detect_encoding()?

I'd prefer a separate utility for this somewhere, since
tokenize.detect_encoding() is not available in Python 2.

I've attached an example implementation with tests, which works
in Python 2.7 and 3.

> On Wed, Mar 16, 2016 at 5:05 PM, Guido van Rossum <guido at python.org> wrote:
>> On Wed, Mar 16, 2016 at 12:59 AM, M.-A. Lemburg <mal at egenix.com> wrote:
>>> The only reason to read up to two lines was to address the use of
>>> the shebang on Unix, not to be able to define two competing
>>> source code encodings :-)
>> I know. I was just surprised that the PEP was sufficiently vague about
>> it that when I found that mypy picked the second if there were two, I
>> couldn't prove to myself that it was violating the PEP. I'd rather
>> clarify the PEP than rely on the reasoning presented earlier here.

I suppose it's a rather rare case, since it's the first time
that I heard about anyone thinking that a possible second line
could be picked - after 15 years :-)

>> I don't like erroring out when there are two different cookies on two
>> lines; I feel that the spirit of the PEP is to read up to two lines
>> until a cookie is found, whichever comes first.
>> I will update the regex in the PEP too (or change the wording to avoid "match").
>> I'm not sure what to do if there are two cooking on one line. If
>> CPython currently picks the latter we may want to preserve that
>> behavior.
>> Should we recommend that everyone use tokenize.detect_encoding()?
>> --
>> --Guido van Rossum (python.org/~guido)

Marc-Andre Lemburg

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