Add lists to class?

[Paolino]

Mike Meyer wrote:
> "BBands" <bbands at gmail.com> writes:
> 
> 
>>I have a list with some strings in in it, 'one', 'two' 'three' and so
>>on. I would like to add lists to a class with those names. I have no
>>way of knowing what will be in the list or how long the list will be in
>>advance.
> 
> 
> Others have told you how to do it. Now I'm going to tell you why you
> shouldn't.
> 
> First, since you don't know the names of the attributes you added, you
> can't possibly write code that references them in the normal way. So
> is there really much point in making them an attribute at all?
> 
> Second, since you don't know the names of the attributes you added,
> you don't know if one of more of them is going to clobber a feafure of
> the class that you want to use for something else. I.e., consider:
> 
> 
>>>>class C:
> 
> ...  pass
> ... 
> 
>>>>c = C()
>>>>print c
> 
> <__main__.C instance at 0x8270b4c>
> 
>>>>c.__str__ = 'foo'
>>>>print c
> 
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> TypeError: 'str' object is not callable
> 
> 
> I.e. - if someone adds a __str__ attribute to your class, you won't be
> able to print it any more. Not a good thing.
> 
> In general, you probably want a dictionary instead of attributes:
> 
> 
>>>>class C(dict):
> 
> ...  def __init__(self, l):
> ...   for i in l:
> ...    self[i] = []
> ... 
> 
>>>>c = C(['a', 'b', 'c'])
>>>>c['a']
> 
> []
> 
and 2c more to use attributes but prevent overriding of real attributes

    def __getattr__(self,name):
      if name in self:
        return self[name]
      raise AttributeError

Paolino

	

	
		
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