Re: Re: extending PersistentList

BTW, i don't know how to contact the admin of this group, but would it be 
possible to change a setting so the writers of posts can edit them (i 
always find typo's etc. after i click post :-). Google says it's possible.

Thanks ..

On Tuesday, May 10, 2016 at 10:35:10 PM UTC+2, Lars van Gemerden wrote:
>
> I am storing the list items in self.items. 
>
> Sequence and its subclass MutableSequence is designed in such a way that 
> by implementing the abstract methods (the methods implemented in 
> PersistentList2), all other standard list methods (like extend, slicing, 
> etc.) follow suit. They basically all call the overridden abstract methods 
> to do the actual item lookup or list mutations. By just overriding these 
> couple of method, e.g. calling extend will also set _p_changed to 1.
>
> The original PersistentList is a subclass of UserList, which is a subclass 
> of MutableSequence as well, but then overrides all methods 
> of MutableSequence, which makes the inheritance pointless. It probably is a 
> little faster though because it less method calls are used. Another 
> disadvantage of this is that if you want to override PersistentList, you 
> likely will have to override or extend all methods, which is error prone, 
> and more code to maintain.
>
> self.owner.__dirty__ = True is a way for me to keep track of changed 
> objects (setting the containing object's __dirty__ to True in a 
> descriptor), for syncing between web clients and server (it needs work 
> though, i am learning somethings from zodb as well ;-). The idea is to use 
> classes in a python client that are (only) defined on the server.
>
> Anyway, thnaks for the feedback. May i conclude that,apart from the 
> MutableSequence stuff, PersistentList2 should work with zodb persistence?
>
> Cheers, Lars
>
>
>
> On Sunday, May 8, 2016 at 1:37:37 PM UTC+2, Christopher Lozinski wrote:
>>
>> At first it all looked too easy. 
>>
>> PersistentList stores the objects in itself, and is complex. It is indeed easier to create 
>> PersistentList2 by pointing to a List object and updating _p_changed.
>>
>> So I will assume that you are storing your objects in the attached list, and not in the 
>> PersistentList2 itself.
>>
>> But then you do not need to subclass off of MutableSequence. Worse yet, 
>> if you do subclass off of 
>> MutableSequence, but only implement some of the methods, for example no 
>> slice methods, if you ever use the slice method, it will execute on the 
>> object itself, and not on the linked to list. 
>>
>> Here are some other comments.
>>
>> It was a great idea to separate out your application code ServerField 
>> List from PersistentList2.  
>>
>> Makes it much easier for us to understand what you are doing, and the 
>> relevance to everyone else. 
>>
>> You did not say what is wrong with Persistent List.  What is it that you 
>> are trying to add.  Maybe someone else
>>
>> has already done it? 
>>
>> What is that  
>>
>>    self.owner.__dirty__ = True
>> all about?
>> Hope that helps.
>> Chris
>>
>>

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