[Python-Dev] Py2.6 buildouts to the set API (original) (raw)

Mike Klaas mike.klaas at gmail.com
Sat May 19 03:50:24 CEST 2007

On 18-May-07, at 6:34 PM, Raymond Hettinger wrote:

Here some ideas that have been proposed for sets:

* New method (proposed by Shane Holloway): s1.isdisjoint(s2). Logically equivalent to "not s1.intersection(s2)" but has an early- out if a common member is found. The speed-up is potentially large given two big sets that may largely overlap or may not intersect at all. There is also a memory savings since a new set does not have to be formed and then thrown away.

+1. Disjointness verification is one of my main uses for set(), and
though I don't think that the early-out condition would trigger often
in my code, it would increase readability.

* Additional optional arguments for basic set operations to allow chained operations. For example, s=s1.union(s2, s3, s4) would be logically equivalent to s=s1.union(s2).union(s3).union(s4) but would run faster because no intermediate sets are created, copied, and discarded. It would run as if written: s=s1.copy(); s.update (s2); s.update(s3); s.update(s4).

It's too bad that this couldn't work with the binary operator spelling:

s = s1 | s2 | s3 | s4

* Make sets listenable for changes (proposed by Jason Wells):

s = set(mydata) def callback(s): print 'Set %d now has %d items' % (id(s), len(s)) s.listeners.append(callback) s.add(existingelement) # no callback s.add(newelement) # callback

-1 on the base set type: it seems too complex for a base set type.
Also, there are various possible semantics that might be desirable,
such as receiving the added element, or returning False to prevent
addition.

The proper place is perhaps a subclass of set with a magic method
(analogous to defaultdict/missing).

-Mike

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