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.
Sorry for the noise,
--
Francesc Alted
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