[Python-ideas] issubclass(collections.OrderedDict, collections.Sequence)

[Ram Rachum]

Use case not relevant enough for you?

On Tue, Oct 7, 2014 at 3:40 AM, Guido van Rossum <guido at python.org> wrote:

> I think I just lost interest in this thread.
>
> On Mon, Oct 6, 2014 at 1:41 PM, Ram Rachum <ram at rachum.com> wrote:
>
>> On Mon, Oct 6, 2014 at 8:35 PM, Guido van Rossum <guido at python.org>
>> wrote:
>>
>>> On Mon, Oct 6, 2014 at 1:10 AM, Ram Rachum <ram at rachum.com> wrote:
>>>
>>>> Here are a couple:
>>>>
>>>>  - I'm making a combinatorics package, and a combination space needs to
>>>> have a __contains__ method that takes a combination and returns whether
>>>> it's part of a set. Since a combination, unlike a permutation, has no
>>>> order, I like to have my combinations be canonicalized in a sorted order.
>>>> For example, in a combination space of 3 items on range(4), (0, 1, 3) would
>>>> be a combination in that space, but (3, 1, 0) would not because it's not
>>>> sorted. (It's a k-permutation but not a combination.) However, if the user
>>>> does `{0, 1, 3} in comb_space` I still want to return True, regardless of
>>>> whether the set iterator happens to give these items in order or not.
>>>>
>>>
>>> So how are you writing this code today? In the following case, what's in
>>> the then or else branch?
>>>
>>> if not isinstance(x, collections.Ordered):
>>>     <what???>
>>> else:
>>>     <what???>
>>>
>>> Even if you could write this, how would you know that an ordered
>>> argument is in the *canonical* order?
>>>
>>
>> That part isn't written yet (the package is still work-in-progress), but
>> I'm not sure what the problem is. I'll have the code look at `x`. If it's
>> marked as ordered, then I'd iterate on it. If it has the correct items
>> (meaning the items of the sequence that this is a combination space of) and
>> the items in x are in the same order as they are in the sequence, and it
>> has the correct number of items, then we have a match. If we have `not
>> isinstance(x, collections.Ordered)` then I do the same thing except I
>> ignore the order of the items. What's the problem?
>>
>>
>>>
>>>  - For the same package, I'm defining `Tally` and `OrderedTally`
>>>> classes. (Simliar to `Counter` except without having an identity crisis
>>>> between being a dict subclass and counter; mine are strictly counters.) In
>>>> the tests I want to easily see whether the class I'm testing is the ordered
>>>> one or not, so I'll know to run appropriate tests. (There are also
>>>> `FrozenTally` and `FrozenOrderedTally` so it's not just one class.) I could
>>>> set `is_ordered = True` on them or give them some base class, but I think a
>>>> general `collections.Ordered` abstract base class would be the best
>>>> solution.
>>>>
>>>
>>> Same question.
>>>
>>> --
>>> --Guido van Rossum (python.org/~guido)
>>>
>>
>>
>
>
> --
> --Guido van Rossum (python.org/~guido)
>
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