PEP 322: Reverse Iteration (second revision, please comment)

[Peter Otten]

Gonçalo Rodrigues wrote:

> - Shouldn't the implementation test for __contains__ instead of
> has_key? e.g.
> 
>     if hasattr(x, "__contains__"):
>         raise ValueError("mappings do not support reverse iteration")
>     etc.
> 
> All my mapping-like classes overload __contains__, never has_key, but
> maybe that's just me.

It won't work:

>>> hasattr([], "has_key")
False
>>>

>>> hasattr([], "__contains__")
True
>>>

Peter