Re: : in the flow context for PyYAML and SnakeYAML

Hi Andrey,

On 08/18/2010 03:13 AM, Andrey Somov wrote:
> Hi all,
> according to http://pyyaml.org/wiki/YAMLColonInFlowContext colon in
> the flow context does not work according to the 1.1 specification in
> PyYAML.
> PyYAML follows "pythonic" way instead of implementing language-neutral
> solution. It causes compatibility issues with other languages.
> There is an issue reported for SnakeYAML to address the problem -
> http://code.google.com/p/snakeyaml/issues/detail?id=78
>
> The ticket for PyYAML is created but there is no progress -
> http://pyyaml.org/ticket/158
>
> I am not really in favor to fix the problem only in SnakeYAML as we
> find it important that any valid document for SnakeYAML is always
> valid for PyYAML and vice versa.


As far as I remember, the YAML 1.1 spec claims that ':' is a valid 
character for a plain literal if it is not followed by a whitespace, and 
the mapping separator is ': ' (colon followed by a whitespace).  I 
strongly disagreed with it because it does not follow Python or 
Javascript conventions, but I didn't want to decide one way or another 
until some consensus is reached.  So I made ':' (colon followed by a 
non-whitespace character) an error when it is a part of a plain literal 
in the flow context.

I haven't checked the YAML 1.2 specs, but I believe the rules were 
relaxed to facilitate JSON compatibility.  AFAIK, the mapping separator 
is now ':' (colon), but colon is still a valid character in a plain 
literal and if it is not followed by a whitespace, it is interpreted as 
a part of the literal rather than a mapping separator.  Thus a JSON 
expression like {"foo":1} is now a valid YAML.  The solution is still 
not that great since a valid Python or Javascript expression like {1:1} 
has a different meaning in YAML (in this case, {'1:1': null}).  I'm not 
sure how much this is a problem in practice though.

I believe there was another proposal (which I like even less): forbid 
':' in mapping keys, but allow them in mapping values.  Unfortunately it 
creates ambiguities in expressions like [foo:bar], which could be 
interpreted both ways.

Note that my understanding of the YAML specs could be incorrect: it was 
a long time ago since I last read them.


Thanks,
Kirill

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