[ZODB-Dev] persistent.py? transaction.py? deriving from PersistentList?

[Alan Ezust]

1. Is it possible to derive from PersistentList and give other attributes to 
derived classes?

2. where is transaction.py?
The http://zope.org/Wikis/ZODB/FrontPage/guide/zodb.html makes reference to an
import transaction
so you can do 
transaction.commit() method, 

but transaction.py

I was told on an IRC that there is a __builtin__ get_transaction() method we 
use instead, but where is that documented in the programming guide?

3. where is persistent.py?
I see ZODB.PersistentList.PersistentList
but not persistent.list.PersistentList (as referenced in 
http://zope.org/Wikis/ZODB/FrontPage/guide/node6.html). Is that another 
package-movement that happened since the last version of that guide?

4. Transaction and PersistentList are both modules with capitalized names, as 
well as classnames. Why? Shouldn't modules be lowercase and classnames 
uppercase? Very Confusing. 

4. I'm having problems with PersistentList.__setslice__. It seems to throw 
exceptions from line 38 of UserList.py

UserList.__setslice__

    def __setslice__(self, i, j, other):
        i = max(i, 0); j = max(j, 0)
        if isinstance(other, UserList):
            self.data[i:j] = other.data
       elif isinstance(other, type(self.data)): # line 38 - self.data is null
            self.data[i:j] = other

It is at this point, self.data is null - does not get properly initialized.

I am calling setslice from a derived class constructor. Perhaps the object is 
not fully initialized yet?

class WebPage(PersistentList)
    """Class WebPage - abstraction for a web page in the database.
        Does not hold onto the contents of the referred page, but does
        cache the links.
    """
    _url = None
    
    def __init__(self, url):
 # at this point, self.data is null - base class ctor not called?
 self[0:3] = ["webpage", {"url" : url}, [], None] 
        self._url = url

I get a null pointer exception here.

How can I derive and extend the PersistentList?

-- 
Alan Ezust  
Victoria, BC