> >>>> a= object() > >>>> (a,) is a > > False > > (a,) is not identical with a. > > >>>> (a,) is (a,) > > False > > The tuple on the left is not identical with the tuple on the right, even > though they are equivalent. > > >>>> a is a > > True > > The variable on the left is identical with the one on the right. This > is not the same comparison as "(a,) is (a,)", which actually contains > the construction of two distinct objects. The moral equivalent of "a is > a" would be: > > >>> b = (a,) > >>> b is b > True > > An interesting thing about Python is that numbers of built-in types are > flyweights. Unlike literals of non-flyweight types, distinct instances > of a given numeric literal actually refer to the same object: > > >>> 5 is 5 > True > >>> 999999999999999999999999999999 is 999999999999999999999999999999 > True > >>> 3.5 is 3.5 > True > > I wonder, will this be true of the upcoming Fraction class? > > >>>> (a,) == (a,) > > True > > The two tuples are equivalent (though not identical). > > >>>> a= [] > >>>> a.append( a ) > >>>> a > > [[...]] > > That's cool. I don't think would have known off the top of my head how > the interactive interpreter would display something like that. Talk > about a cyclic reference... > > >>>> tuple(a) is tuple(a) > > False > > The tuple on the left is not identical with the tuple on the right, even > though they are equivalent. This is the sample as one of your earlier > examples, just with slightly different syntax. > > > hasVanilla= True > > hasStrawberry= True > > hasChocolate= True > > if hasVanilla: > > print "Vanilla" > > if hasVanilla and not hasChocolate: > > print "and" > > if hasStrawberry: > > print "Strawberry" > > if hasVanilla or hasStrawberry and hasChocolate: > > print "and" > > if hasChocolate: > > print "Chocolate." > > You've tried to implement a set using a set of flags to indicate whether > various items have membership in that set. See how an object > representing a given flavor would have to be distinct from the object > (boolean flag) indicating its set membership? Btw, your formatting > could use some work. :) Some flavor combinations cause extra "ands" to > be printed. Here's a little test harness, with PEP-friendly variable > names, and showing how your booleans corresponding directly with > traditional bit-bucket flag sets: > > def print_flavors(flags): > > print flags > > vanilla = flags & 1 > strawberry = flags & 2 > chocolate = flags & 4 > > if vanilla: > print "Vanilla" > if vanilla and not chocolate: > print "and" > if strawberry: > print "Strawberry" > if vanilla or strawberry and chocolate: > print "and" > if chocolate: > print "Chocolate." > > if __name__ == '__main__': > for flavor_flags in range(8): > print_flavors(flavor_flags)- Hide quoted text - > > - Show quoted text -
while True: "No, it's the element." "No, it's a tuple with one element." -- http://mail.python.org/mailman/listinfo/python-list
