<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Mon, Oct 6, 2014 at 1:10 AM, Ram Rachum <span dir="ltr"><<a href="mailto:ram@rachum.com" target="_blank">ram@rachum.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Here are a couple:<div><br></div><div> - 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. </div></div></blockquote><div><br></div><div>So how are you writing this code today? In the following case, what's in the then or else branch?<br><br>if not isinstance(x, collections.Ordered):<br></div><div> <what???><br></div><div>else:<br></div><div> <what???><br><br></div><div>Even if you could write this, how would you know that an ordered argument is in the *canonical* order?<br></div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div> - 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.</div></div></blockquote><div><br></div><div>Same question.<br><br></div></div>-- <br>--Guido van Rossum (<a href="http://python.org/~guido">python.org/~guido</a>)
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