"Duncan Booth" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > [EMAIL PROTECTED] wrote: > > > After much head scrating and experimenting with dis.dis() I have found > > that chaining comparisons (with is or ==) a == b == c in Python is > > never a good idea. It is interpreted as > > ( a == b ) and ( b == c) > > Such a magic is fine when we write: > > if 0.0 <= x < 1.0: > > but it renders the outcome of if a == b == c: somewhat confusing. > > I don't understand why it is confusing. What other meaning would you > expect?
I can see how one might get themselves confused. I think it simply boils down to thinking that A == B == C is shorthand for: (A == B) == C It's not. You're asserting that A is equivalent to B and B is equivalent to C, NOT that the value of comparing A to B is equivalent to C: >>> False is False True >>> False is False is True False If what you want is the second form, a pair of parenthesis forcing order of evaluation will give it to you. >>> (False is False) is True True -ej -- http://mail.python.org/mailman/listinfo/python-list
