Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #36897 > unrolled thread

Using inner dict as class interface

Back to article view | Back to comp.lang.python

Contents

  Using inner dict as class interface Florian Lindner <mailinglists@xgm.de> - 2013-01-16 15:42 +0100
    Re: Using inner dict as class interface Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-01-16 14:54 +0000
      Re: Using inner dict as class interface Peter Otten <__peter__@web.de> - 2013-01-16 18:34 +0100

#36897 — Using inner dict as class interface

Hello,

I have a:

class C:
   def __init__(self):
      d = dict_like_object_created_somewhere_else()

  def some_other_methods(self):
    pass


class C should behave like a it was the dict d. So I could do:

c = C()
print c["key"]
print len(c)

but also

c.some_other_method()

How can I achieve that? Do I need to define all methods like
__getitem__, __len__, ... (what else?) to access the inner dict or is
there something more slick?

Thanks,

Florian

[toc] | [next] | [standalone]

#36900

On Wed, 16 Jan 2013 15:42:42 +0100, Florian Lindner wrote:

> Hello,
> 
> I have a:
> 
> class C:
>    def __init__(self):
>       d = dict_like_object_created_somewhere_else()
> 
>   def some_other_methods(self):
>     pass
> 
> 
> class C should behave like a it was the dict d. 

Then make it a dict:

class C(dict):
    def some_other_methods(self):
        pass

my_dict = C(key="value")  # or C({"key": "value"})
print len(my_dict)
print my_dict['key']
my_dict.some_other_methods()



-- 
Steven

[toc] | [prev] | [next] | [standalone]

#36909

Steven D'Aprano wrote:

> On Wed, 16 Jan 2013 15:42:42 +0100, Florian Lindner wrote:
> 
>> Hello,
>> 
>> I have a:
>> 
>> class C:
>>    def __init__(self):
>>       d = dict_like_object_created_somewhere_else()
>> 
>>   def some_other_methods(self):
>>     pass
>> 
>> 
>> class C should behave like a it was the dict d.
> 
> Then make it a dict:
> 
> class C(dict):
>     def some_other_methods(self):
>         pass
> 
> my_dict = C(key="value")  # or C({"key": "value"})
> print len(my_dict)
> print my_dict['key']
> my_dict.some_other_methods()

If for some reason it is impractical to follow Steven's advice you can 
subclass collections.Mapping or collections.MutableMapping. That should give 
you a clear notion of the required methods and has defaults for some of 
them.

>>> class A(Mapping): pass
... 
>>> A()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Can't instantiate abstract class A with abstract methods 
__getitem__, __iter__, __len__
>>> class B(Mapping):
...     def __getitem__(self, key):
...             return {1:2}[key]
...     def __len__(self): return 1
...     def __iter__(self): yield 1
... 
>>> b = B()
>>> list(b)
[1]
>>> b.items()
[(1, 2)]

[toc] | [prev] | [standalone]

Back to top | Article view | comp.lang.python

csiph-web