Re: using yaml_constructors attribute of the Loader class

Manlio Perillo wrote:
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> 
> Kirill Simonov ha scritto:
>> Manlio Perillo wrote:
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>>>
>>> Hi.
>>>
>>> In a framework I'm writing I have a custom YAML Loader, with several
>>> custom constructors.
>>>
>>> Now, I would like to allow applications to define their own
>>> constructors, and have them be used by my framework.
>>>
>>> Using setuptools entry points, the code is something like this:
>>>
>>>
>>> from pkg_resources import iter_entry_points
>>> from yaml.loader import Loader
>>>
>>> class MyLoader(Loader):
>>>     def factory(cls)
>>>         yaml_constructors = cls.yaml_constructors
>>>         for ep in iter_entry_points('my.entrypoint'):
>>>             yl = ep.load()
>>>
>>>             yaml_constructors.update(yl.yaml_constructors)
>>>
>>>         d = dict(yaml_constructors=yaml_constructors)
>>>         return type('MyLoader', (cls,), d)
>>>
>>> Applications just need to create a custom loader class, derived from
>>> yaml.loader.Loader, and register their own constructors.
>>>
>>> Is it "safe" (that is, is the API stable) to access the
>>> yaml_constructors attribute of the Loader class?
>>>
>> Well, `yaml_constructors` is not a part of the documented API, but I
>> don't think it's going to be removed any time soon.  In the worst case,
>> you could always add a check for yaml.__version__:
>>
>> if yaml.__version__ < 'X.Y':
>>     # Use yaml_constructors here
>> else:
>>     # Use the brand new API here.
>>
> 
> My concern is that the new API will not allow me to do what I'm doing now.
> 
> As an example, if add_constructor is written in C and will store the
> dictionary in C code, so that registered constructors are no more
> accessible from Python code.
> 

I think using yaml_constructors is reasonably safe.

In any case, I don't have any time to refactor the pyyaml api, which is 
a shame; there are several problems that I'd love to have fixed.

> 
> By the way, is yaml_constructors in old versions?
> 

Yes, yaml_constructors is in pyyaml since the initial release.


Thanks,
Kirill

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