Is there a canonical way to check whether an iterable is ordered?
alister.nospam.ware at ntlworld.com
Fri Sep 19 14:26:19 CEST 2014
On Fri, 19 Sep 2014 21:56:05 +1000, Chris Angelico wrote:
> On Fri, Sep 19, 2014 at 9:46 PM, Steven D'Aprano
> <steve+comp.lang.python at pearwood.info> wrote:
>> Chris Angelico wrote:
>>> On Fri, Sep 19, 2014 at 8:59 PM, Steven D'Aprano
>>> <steve+comp.lang.python at pearwood.info> wrote:
>>>> Here's a proof of concept of what would be allowed:
>>> Also, this can't possibly offer the same guarantee. Watch:
>>> d = MyDict(some_lot_of_items)
>>> d.values(); d.items()
>>> # mutate the dict in whatever way you like pairs = zip(d.keys(),
>>> This might well create mismatched pairs, because after generating the
>>> keys() return value, the list gets shuffled, prior to generating
>>> values() in the same expression. This would not be allowed.
>> That would be a bug, and an easy one to fix. Every mutation of the dict
>> would have to reset the internal flags back to the starting state.
> What if there's no mutation, then? Just calling values() and items()
> means that the zip of keys and values will make mismatches.
As far as I understand it the order of keys in a dict is not guaranteed
iterating over the same dict twice (without changes) does not have to
return the keys in the same order.
In my installation of python the order does remain constant unless the
dict is modified but I am reasonably sure this is just due to
implementation detail & should not be relied upon.
As simple amateur I may be mistaken.
"Tell the truth and run."
-- Yugoslav proverb
More information about the Python-list