Re: [Pytables-users] Why have column descriptors to be given as classes!?!

[Norbert N. <Nor...@gm...>]

Stupid me! It's there already...



Am Sonntag, 16. Januar 2005 14:12 schrieb Norbert Nemec:
> Hi there,
>
> just considered using Tables instead of Arrays for my purpose. Now I really
> had to fight the fact that column descriptors have to be given as classes.
>
> Problem is: defining a class the regular way means, that at the time of
> writing a python script, you have to know the names and types of all
> columns. If you get the names of the columns as strings from some other
> source, this becomes considerably harder.
>
> The hack I've come up with for the moment looks like:
>
> -----------------------------------------------------------
> #!/usr/bin/env python
>
> from tables import *
>
> def descfromdict(__d__):
>     class res(IsDescription):
>         for __k__ in __d__:
>             locals()[__k__] = __d__[__k__]
>     return res
>
> file = openFile('tryout.h5','w')
>
> mydict={}
> mydict['somecolumn'] = FloatCol()
> mydict['transmission'] = FloatCol()
> mydict['statistics'] = UInt16Col()
>
> file.root.mytable = Table(descfromdict(mydict))
>
> file.close()
> ---------------------------------------------
>
> similarly, it would be possible to us an object instead of a class, which
> would even allow natural naming:
>
> ------------------------------------------------------
> #!/usr/bin/env python
>
> from tables import *
>
> def descfromobj(__d__):
>     class res(IsDescription):
>         for __k__ in __d__.__dict__:
>             locals()[__k__] = getattr(__d__,__k__)
>     return res
>
> class MyDescription:
>     def __setitem__(self,key,value):
>         assert type(key) is str
>         assert isinstance(value,Col)
>         setattr(self,key,value)
>
>
>
> file = openFile('tryout.h5','w')
>
> myobj = MyDescription()
> myobj.somecolumn = FloatCol()
> myobj['anothercolumn'] = FloatCol()
>
> file.root.mytable = Table(descfromobj(myobj))
>
> file.close()
> --------------------------------------------
>
> Both work, but it is really ugly if you have to find such a solution
> yourself.
>
> In the least, I would suggest to offer these options as an alternative way
> to pass descriptions. But I would think, that it would simplify things a
> lot, if one of these methods (or something even better) would become the
> preferred and documented way of passing a descriptor and the old method of
> defining and passing a class be obsoleted. I think, even the internals of
> pytables might be simplified by it...
>
> Ciao,
> Norbert

-- 
_________________________________________Norbert Nemec
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