Ian Kelly wrote: > On Thu, Jul 25, 2013 at 2:13 AM, Peter Otten <__pete...@web.de> wrote: >> Chris Angelico wrote: >> >>> On Thu, Jul 25, 2013 at 5:04 PM, Steven D'Aprano >>> <steve+comp.lang.pyt...@pearwood.info> wrote: >>>> - Views support efficient (O(1) in the case of keys) membership >>>> testing, which neither iterkeys() nor Python2 keys() does. >>> >>> To save me the trouble and potential error of digging through the >>> source code: What's the complexity of membership testing on >>> values/items? Since you're calling it "efficient" it must be better >>> than O(n) which the list form would be, yet it isn't O(1) or you >>> wouldn't have qualified "in the case of keys". Does this mean >>> membership testing of the values and items views is O(log n) in some >>> way, eg a binary search? >> >> keys() and items() is O(1); both look up the key in the dictionary and >> items() then proceeds to compare the value. values() is O(n). > > 3.x values() is O(n) but avoids the unnecessary step of copying all the > values in the dict that you get when performing the same operation > using 2.x values(). Hence, although the asymptotic complexity is the > same, it's still more efficient.
In Python 2 the prudent pythonista used itervalues() to avoid unnecessary intermediate list... -- http://mail.python.org/mailman/listinfo/python-list
