[cctbxbb] boost python and metaclass inheritance

[David Waterman]

Hi Luc,

Actually it almost works, because Refinery should not inherit
from normal_eqns.non_linear_ls, only the adapter, AdaptLstbx. So I can do:

import abc
from scitbx.lstbx import normal_eqns

class Refinery(object):
  __metaclass__ = abc.ABCMeta
  pass

class AdaptLstbx(Refinery, normal_eqns.non_linear_ls):
  class __metaclass__(normal_eqns.non_linear_ls.__class__, abc.ABCMeta):
pass
  pass

This successfully stops Refinery being constructed. However, you do point
out the critical flaw, which is that AdaptLstbx can now be constructed, yet
this still lacks the missing 'run' method, which would be supplied another
child. Now the original raise NotImplementedError() seems like the clearest
solution. I suppose this is why people on the internet argue that abc isn't
pythonic.

Cheers

-- David


On 9 January 2014 00:48, Luc Bourhis <luc_j_bourhis at mac.com> wrote:

> > import abc
> > from scitbx.lstbx import normal_eqns
> > class Refinery(object):
> >  class __metaclass__(normal_eqns.non_linear_ls.__class__, abc.ABCMeta):
> pass
> >
> > class AdaptLstbx(Refinery, normal_eqns.non_linear_ls): pass
>
> Except that it does not prevent
>   r = Refinery()
> after all since the __metaclass__ has a valid instantiation through
> normal_eqns.non_linear_ls.__class__.
>
> which gives me a flashback: I've already burnt myself with that!
>
> Luc
>
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