[Python-3000] Spooky behavior of dict.items() and friends

[Mike Klaas]

On 2-Apr-08, at 3:48 PM, Martin v. Löwis wrote:
>> On Wed, Apr 2, 2008 at 5:08 PM, Mike Klaas <mike.klaas at gmail.com>  
>> wrote:
>>> ...and the majority of these cases would work fine with views (input
>>> to sorted(), etc).
>>
>> Suppose "the majority" here means 36 of the 46 cases.
>
> What makes you suppose so. In the standard library of Python 2.5, I
> could not find a single case where using views would cause silent
> breakage:
> - the majority of uses is in for loops or list comprehensions.
> - of the remaining uses, the majority is with .sort(), which
>  would cause an exception, to be rewritten as sorted(foo.items())
> - of the then-remaining cases, the majority is immediately followed
>  by an iteration, with no intermediate changes to the dictionary.
> - in some cases, the view is returned to the caller (i.e. outside
>  of the standard library); whether this would break anything would
>  depend on the application.
>
> In your code, how many (in absolute numbers) applications of .items()
> would break when .items() becomes a view?

I assume you are asking Jason even though you attributed the quote to  
me.

However, a cursory examination of the 46 non-'for' I quoted above  
results in a situation much like you describe: either silently working  
fine with view, or louding breaking where a list was expected.  There  
are some that get passed out of functions which may fail silently but  
I don't have time to examine them in detail right now.

-Mike