[Fwd: Re: managed lists?]

[Jorgen Bodde]

Hi Gabriel,

Yep that basically covered my implementation as well. It was rather
trivial to make it, and even for a python newbie it was simple which
says enough about the language itself. ;-)

Although I understand the opinions that you should not care about
types, I do believe putting a constraint on the list by either class
type or interface spec, is no bad thing. The interface specification
is hard to realise as this list now functions as some kind of template
class (hence the parameter that specifies which type is allowed).

I also added callback arguments that are called opon when there are
items added to the list, deleted or when it is cleared so that the
main object gets notified when another object changes it.

Here is my implementation (I bet it can be done better, but I am only
playing with python since about 3 months now):

--------------------------

class ObjListException(Exception):
    pass

class ObjListIterator(object):
    def __init__(self, objlist):
        self.__objlist = objlist
        self.__idx = 0

    #---------------------------------------------------------------------------
    def __iter__(self):
        return self

    #---------------------------------------------------------------------------
    def next(self):
        result = None
        if self.__idx >= len(self.__objlist):
            raise StopIteration()
        else:
            result = self.__objlist[self.__idx]
            self.__idx += 1
        return result

#===============================================================================

""" ObjList - A managed somewhat strong typed list for Python.
    Expects {object}._id to be a property """

class ObjList(object):
    def __init__(self, class_name, add_callback = None,
                 remove_callback = None, clear_callback = None):
        self.__list = []
        self.__cname = class_name
        self.__add_cb = add_callback
        self.__remove_cb = remove_callback
        self.__clear_cb = clear_callback

    #---------------------------------------------------------------------------
    def __iter__(self):
        return ObjListIterator(self.unmanaged_list())

    #---------------------------------------------------------------------------
    def __getitem__( self, key):
        if key < len(self.__list) and key >= 0:
            return self.__list[key]
        return None

    #---------------------------------------------------------------------------
    def clear(self):
        self.__list = []

    #---------------------------------------------------------------------------
    def append(self, obj):
        if isinstance(obj, self.__cname):
            if obj not in self.__list:
                self.__list.append(obj)
                if self.__add_cb:
                    self.__add_cb(self, obj)
        else:
          raise ObjListException()

    #---------------------------------------------------------------------------
    def remove(self, obj):
        if obj in self.__list:
            self.__list.remove(obj)
            if self.__remove_cb:
                self.__remove_cb(self, obj)

    #---------------------------------------------------------------------------
    def count(self):
        return len(self.__list)

    #---------------------------------------------------------------------------
    def unmanaged_list(self):
        return self.__list[:]

    #---------------------------------------------------------------------------
    def find_id(self, id):
        for i in self.__list:
            if i._id == id:
                return i
        return None

    #---------------------------------------------------------------------------
    def has_item(self, obj):
        if obj in self.__list:
            return True
        return False

    #---------------------------------------------------------------------------
    def append_many(self, lst):
        for l in lst:
            self.append(l)

Regards,
- Jorgen