[Python-Dev] DRAFT: pydev summary for 2006-12-01 to 2006-12-15

[Walter Dörwald]

Calvin Spealman wrote:

> [...]
> -----------------------------------
> Creating dicts from dict subclasses
> -----------------------------------
> 
> A common problem of subclassing built-in types (dict, in this case) arose trying
> to move weakref.WeakValueDictionary to a subclass of dict, rather than UserDict.
> 
> [NOTE: Could someone give a better description of this? I don't know enough of
> the issue here to write any content full enough. Thanks.]

The problem is that if you pass a mapping (i.e. something with a keys() 
method) to the dict constructor, it uses keys() and __getitem__() to 
make a copy. However if the argument is a subclass of dict, any 
overwritten keys() or __getitem__() methods are ignored.

Servus,
    Walter