Recommended data structure/ implementation

[Gabriel Genellina]

En Wed, 13 Feb 2008 05:34:43 -0200, Mike D <42flicks at gmail.com> escribió:

> I have a simple requirement: A user belongs to groups and groups contain
> items.
>
> Based on user/group I want to display items.
> Based on user I want to display groups.
>
> What would be the best method of implementing this? A dictionary of  
> objects?
>
> I'd usually just use a database but I feel it's quite unnessacary and  
> its a
> scenario I'd like to know the solution for.

Assuming there is no inherent ordering in groups nor items, I'd use a set  
for both.

py> class Group(object):
...     def __init__(self, name):
...         self.name = name
...         self.items = set()
...     def __repr__(self):
...         return '%s(%r)' % (self.__class__.__name__, self.name)
...
py> class User(object):
...     def __init__(self, name):
...         self.name = name
...         self.groups = set()
...     def __repr__(self):
...         return '%s(%r)' % (self.__class__.__name__, self.name)
...     def all_items(self):
...         result = set()
...         for group in self.groups:
...             result.update(group.items)
...         return result
...
py> gA = Group('A')
py> gA.items.add('Item One')
py> gA.items.add('Item Two')
py> gB = Group('B')
py> gB.items.update(['Item Three','Item Four','Item Five'])
py> gC = Group('C')
py> gC.items.update(['Item Six','Item Seven'])
py>
py> piluso = User('piluso')
py> piluso.groups.add(gA)
py> piluso.groups.add(gB)
py> coquito = User('coquito')
py> coquito.groups.add(gB)
py> coquito.groups.add(gC)
py>
py> print piluso, piluso.groups
User('piluso') set([Group('A'), Group('B')])
py> print coquito, coquito.groups
User('coquito') set([Group('B'), Group('C')])
py> print "group B items:", gB.items
group B items: set(['Item Three', 'Item Five', 'Item Four'])
py> print "groups B and C items:", gB.items | gC.items
groups B and C items: set(['Item Seven', 'Item Six', 'Item Three
', 'Item Four', 'Item Five'])
py> print "coquito's items:", coquito.all_items()
coquito's items: set(['Item Seven', 'Item Six', 'Item Three', 'I
tem Four', 'Item Five'])
-- 
Gabriel Genellina