PersistentList (ZODB)

[Mike C. Fletcher]

Python isn't variable-typed, it's object-typed...

    a = b

does not convert b to some particular type depending on 'a', and 
probably won't unless/until we also get (hopefully optional) type 
declarations for attributes.  However:

    a[:] = b

(replace all elements in a with the contents of b) might work for you. 
 Or, if you feel like it, you can use something like basicproperty, 
which allows you to declare that a particular attribute of an object has 
a particular type/class (and will be coerced to that type if necessary) 
so that:

    d.a = b

would do the conversion.  However, that only works with ZODB4 (with Zope 
3).  You could probably cobble something together with __setattr__ hooks 
for ZODB3 (Zope 2.x) that would do the same thing less elegantly.  I 
find, with basicproperty (which takes Python 2.2.2 properties and allow 
you to declare types, upper/lower-bounds and the like for them) and 
ZODB4 persistence is largely a "don't care" issue (modulo a few 
annoyances regarding transaction boundaries for long-running connections).

Good luck,
Mike

Thomas Guettler wrote:

>Hi!
>
>I use PersistentList v1.3 from Zope2.6.
>
>If I do the following
>
>mylist=PersistentList()
>type(mylist)
>mylist.append(5)
>mylist=[1, 2, 3] # (*)
>type(mylist)
>
>mylist is not a PersistentList anymore. Is there
>a way to change PersistentList that way that the line
>marked with (*) does not delete the PersistentList,
>but creates a new empty one?
>
>This would bring me one big step towards programming nirvana:
>     "Don't care for persistence!"
>
> thomas
>
>  
>

-- 
_______________________________________
  Mike C. Fletcher
  Designer, VR Plumber, Coder
  http://members.rogers.com/mcfletch/