On Mar 29, 12:56 pm, Steven D'Aprano <[EMAIL PROTECTED]> wrote: > On Wed, 28 Mar 2007 18:16:31 -0700, s99999999s2003 wrote: > > what do you mean by create new object when using list comprehensoin or > > list()? Does using slicing create a new object as well? > > Yes it does. > > >>> alist = [1, 2, 4, 8, 16] > >>> blist = alist # not a copy > >>> id(alist) == id(blist) > True > >>> blist = alist[:] # a copy > >>> id(alist) == id(blist) > > False > > By the way, "id(obj) == id(another_object)" is just a long way of writing > "obj is another_object". > > In general: > > - use a list comprehension when you need to calculate the list items > > - use slicing when you are copying an actual list, or if you don't care > what type of object you get > > - use the list() function when your existing object might not be an actual > list, and you want the copy to be a list. > > E.g. > > atuple = (1, 2, 3) > alist = [2*n+3 for n in atuple] > btuple = atuple[:] > blist = list(atuple) > > -- > Steven.
hi thanks under what circumstances do we need to create a copy of a tuple :-> "btuple = atuple[:]". tuples are immutable, so wouldn't it be "wasting memory"? another query, in the docs, list(a) and a[:] does the same thing (a = [1,2,3] for example), but besides the speed of slicing is faster than list(), what advantage is there for using list(a) in this case ? thanks -- http://mail.python.org/mailman/listinfo/python-list
