Steven D'Aprano wrote: > James Dennett wrote: > >> > Yes: 5^2 + -2^2 is 29, however you write it. >> >> *If* you take -2 as a number, but not if you take the number >> as 2 and the unary minus as an operator with lower precedence >> than exponentiation. > > > [snip] > >> Not in this respect. However, the question is whether that's >> a unary -, which binds lower than exponentiation in most systems, >> or part of the negative number minus 2. > > > In Python, all numbers are positive. -2 is a unary minus in front of 2.
Indeed, as I hoped was clear from the rest of my post. When we're discussing what the rules of Python *should* be, however, it's necessary to step back and not assume that the rules of Python are "right", whatever we might mean by that. I was illustrating that the choice made by Python in this respect, i.e., of viewing "-2" as an expression where unary minus applies to the number 2, naturally leads to 5**2 + -2**2 being evaluated as 21 (because of the precedence of unary minus), whereas taking "-2" as a number would lead to the answer 29 (which is not what Python gives). That said, Python's choice is consistent with conventional mathematical notation, which is one reason not to lex -2 as a number in a language with an infix exponentiation operator. -- James -- http://mail.python.org/mailman/listinfo/python-list
