Re: : in the flow context for PyYAML and SnakeYAML

This is the C version of libYAML, looked up in my raw version of the 
downloaded code from http://pyyaml.org/download/libyaml/yaml-0.1.3.tar.gz

The source code file scanner.c contains several examples where it does 
not require a space after a ':' if inside a "flow" (meaning inside curly 
or square brackets). "parser->flow_level" is non-zero in this case.

The function yaml_parser_fetch_next_token() has this code to see if we 
are looking at a colon (called a "value indicator"). I am unsure if this 
code is actually called when using the parser however:

     /* Is it the value indicator? */

     if (CHECK(parser->buffer, ':')
             && (parser->flow_level || IS_BLANKZ_AT(parser->buffer, 1)))
         return yaml_parser_fetch_value(parser);

The function yaml_parser_scan_plain_scalar() uses the following code to 
decide if a character ends an unquoted scaler. Besides skipping a test 
for space after the colon, this also causes the characters ",?[]{}" to 
end a scaler. I know for a fact that this code is used:

             /* Check for indicators that may end a plain scalar. */

             if ((CHECK(parser->buffer, ':') && 
IS_BLANKZ_AT(parser->buffer, 1))
                     || (parser->flow_level &&
                         (CHECK(parser->buffer, ',') || 
CHECK(parser->buffer, ':')
                          || CHECK(parser->buffer, '?') || 
CHECK(parser->buffer, '[')
                          || CHECK(parser->buffer, ']') || 
CHECK(parser->buffer, '{')
                          || CHECK(parser->buffer, '}'))))
                 break;


Kirill Simonov wrote:
> Hi William,
> 
> On 08/24/2010 08:32 PM, William Spitzak wrote:
>> libyaml, which I thought was following the spec, quite specifically does
>> not require a ':' in a "flow" context. There is code in there that
>> literally says it is doing this, so somebody thought it was correct.
>>
>> Here is a conversion using the event api of libyaml to read and write
>> some 1-line files (the output has "flow" and all quoting forced on to
>> make it understandable):
>>
>> a:1 -> "a:1"
>> a: 1 -> {"a": "1"}
>> {a:1} -> {"a": "1"}
>> {a: 1} -> {"a": "1"}
>>
>> So libyaml is doing what I think is being requested.
> 
> Not sure how you get these.  The first two examples and the last one are 
> non-controversial.  However I'm getting a scanner error on {a:1}:
> 
>  >>> import yaml
>  >>> yaml.load("{a:1}", Loader=yaml.CLoader)
> Traceback (most recent call last):
>   [...]
> yaml.scanner.ScannerError: while scanning a plain scalar
>   in "<byte string>", line 1, column 2
> found unexpected ':'
>   in "<byte string>", line 1, column 3
> 
> Note that CLoader uses libyaml bindings internally.
> 
> Perhaps you are using some patched version of libyaml?
> 
> 
> Thanks,
> Kirill

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