On 2009-12-18, at 05:28, Francesc Alted wrote:
> A Friday 18 December 2009 11:54:49 Maarten Sneep escrigué:
>> On 18 dec 2009, at 11:43, Francesc Alted wrote:
>>> Hi List,
>>>
>>> I'm about to merge the links branch into trunk, but suddenly it
>>> occurred
>>> to me a new idea on how to dereferring soft/external links.
>>> Currently,
>>> these links work like this:
>>>
>>> f = tb.openFile('links.h5', 'w')
>>> g = f.createGroup('/', 'g')
>>> a1 = f.createCArray(g, 'a', tb.Int64Atom(), shape=(10000,))
>>> la = f.createSoftLink('/', 'la', '/g/a') # /la points to /g/a
>>>
>>> and dereferring la is implemented via the `__call__()` method:
>>>
>>> a2 = la() # a2 is the 'a' CArray
>>>
>>> But I think now that perhaps it would be better to implement
>>> dereferencing via a property (say `target`):
>>>
>>> a2 = la.target # a2 is the 'a' CArray
>>>
>>> That would allow to natural naming to work even through links
>>> referring
>>> to groups. For example, if lg
>>>
>>> lg = f.createSoftLink('/', 'lg', '/g') # /lg points to /g
>>>
>>> then we could do:
>>>
>>> a3 = f.root.lg.target.a # a3 is the 'a' CArray
>>>
>>> which I think is consistent with the way that PyTables uses to
>>> access
>>> nodes. What people think?
>>
>> Hi,
>>
>> Do it in a way that doesn't require me to know if it is a link or
>> not,
>> group or otherwise. Of course when writing you will know, but not
>> when
>> using. I think that means I prefer the first method.
>
> Thanks for your feedback Maarten.
>
> Hard links already implement your suggested way that doesn't require
> to know
> if it is a link or not (in fact, hard links are just meant for
> providing
> different paths to the same node). However, soft and external links
> *do* need
> to have a different personality than the nodes they point to. This
> is because
> you need to know that, say, '/path/to/node' is a link or not in
> order to know
> the different instance variable or methods that you can use.
>
>> In addition you can add a property to manipulate the link itself,
>> but not
>> for normal use of the data.
>
> Unfortunately, I think I cannot go the property venue. In the
> middle of the
> property implementation I realized that an external link needs a way
> to pass
> parameters to the dereferring method. For example, if:
>
> la = f.createExternalLink('/', 'lg', 'externalfile.h5:/g')
>
> then we can derefer the link is several ways:
>
> la() # open external file in 'r'ead-only mode (default)
> la('a') # open external file in 'a'ppend mode
> la(METADATA_CACHE_SIZE=2**24) # open external file with specific
> param
>
> And as it would be desirable to have the same interface for soft and
> external
> links, then I think I'll stick with the special `__call__` method
> for the
> moment.
>
If __call__ means 'open', then wouldn't it be clearer (more explicit)
to just have a method named open?
> Sorry for the noise,
>
> --
> Francesc Alted
>
Ted
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