On 2-Apr-08, at 2:59 PM, Martin v. Löwis wrote:
> Jason Orendorff wrote:
>> On Tue, Apr 1, 2008 at 9:37 PM, "Martin v. Löwis"
>> <[EMAIL PROTECTED]> wrote:
>>> I think it's fairly obvious why the 2.x .keys() has to change. It's
>>> just too wasteful to actually build the list of all keys of a
>>> dictionary
>>> (or even of all values, as you have to create all the tuples as
>>> well),
>>> if all you want to do is to iterate over it, and the most common
>>> operation of .keys() is to iterate over it in a for look (right?).
>>
>> I don't think so. Is this a use case for d.keys()? Why not just
>> write "for k in d"?
>
> See the subject. What do you say about d.items()?
Exactly. Iterating over the items of a dictionary is one of the most
common dict operations, especially in list/genexp contexts.
$ pygrep '\.items' | wc -l
128
$ pygrep '\.iteritems' | wc -l
211
This may make it seem like iteration is only twice as common, but the
majority of .items() use is in for loops where iteration is more
appropriate. There are only 46 non-'for' uses of .items() in this
codebase:
$ pygrep '\.items' | grep -v for | wc -l
46
...and the majority of these cases would work fine with views (input
to sorted(), etc). Needing a physical list snapshot of them items
that will be used independently of the dictionary is a much rarer use
case. It is good that this will be distinguished from the iteration
use-cases with the extra syntax list(d.items()).
-Mike
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