Paul Rubin wrote: > Jeff Schwab <[EMAIL PROTECTED]> writes: >>>> In CS, a tuple is a kind of data structure that is specifically not >>>> identical with any of its elements. That's the sort of tuple used in >>>> Python. > > The usual CS meaning of "tuple" is more like the physics meaning than > like the Python meaning, I think.
That has not been my experience. >>>>>> (a,) is (a,) >>> False >> The tuple on the left is not identical with the tuple on the right, >> even though they are equivalent. > > Implementation artifact. It could be constant folded. > x = (a,) > y = x > x is y > should print True. I gave a similar example, but you snipped it. >> 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 > > Again an implementation artifact, not guaranteed by the language. Try: > (5+1) is (5+1) True > then try > (999999999999999999999999999999+1) is (999999999999999999999999999999+1) False I think you're a little confused about the meaning of "numeric literal." (5+1) is not a numeric literal. Neither is (999999999999999999999999999999+1). The flyweight pattern does not guarantee that all equivalent instances of an object type will be identical. Maybe I should have said that *some* distinct instances of a given numeric literal actually refer to the same object, so as not to imply that *all* of them did. I don't know whether 5 is always guaranteed to be the same object as any other 5 in a given Python session. -- http://mail.python.org/mailman/listinfo/python-list
