Avetis KAZARIAN <aveti...@gmail.com> wrote: >It seems that any strict ASCII alpha-numeric string is instantiated as >an unique object, like a "singleton" ( a =3D "x" and b =3D "x" =3D> a is b = >) >and that any non strict ASCII alpha-numeric string is instantiated as >a new object every time with a new id.
What no-one appears to have mentioned so far is that the purpose of this implementation detail is to ensure that there is a single instance of strings which are valid identifiers, so that you don't go around creating and destroying string instances just to do an attribute look-up on an object. A few strings which are not valid as identifiers get swept up into this system: >>> a = "1" >>> b = "1" >>> a is b True "Small" integers get a similar treatment: >>> a = 256 >>> b = 256 >>> a is b True >>> a = 257 >>> b = 257 >>> a is b False But as as hopefully been made clear, all this is completely an implementation detail. (Indeed, the range of "interned" integers changed from 0--99 to -5--2356 a few versions ago.) So don't, under any circumstances, rely on it, even when you understand what's going on. -- \S under construction -- http://mail.python.org/mailman/listinfo/python-list
