On Thursday, January 30, 2014 8:39:03 PM UTC+5:30, Steven D'Aprano wrote: > On Thu, 30 Jan 2014 09:08:58 -0500, Roy Smith wrote:
> > 1) Assume that you don't have the full operator precedence table > > memorized and just parenthesize everything. > Oh really? Do you actually write stuff like this? > b = ((2*a) + 1) > if (b >= (-1)): > ... > I would hope not. > > 2) In cases where the expression is so simple, you couldn't possibly be > > wrong, see rule #1. > Or, you can avoid superstitious responses *wink* > (1) Learn the operator precedences to the best of your ability. It's > not hard, most of it works just like the precedences you're used > to from maths class (remember that?) or in the most intuitively > useful way. > E.g. `1 + x == 2` does the useful thing of calculating 1 + x > before testing for equality, rather than the stupid thing of > calculating x == 2 first then adding it to 1. > (2) When in doubt, use parentheses. > (3) When the expression is complex, a few extra parentheses can > help make it easier to understand. "Seven, plus or minus two" > is (roughly) the number of distinct items the human short- > term memory can hold. Grouping terms together can help reduce > the distinct number of items the reader needs to keep in > short-term memory. > E.g. `x+1 > 0 and y >= 5` is potentially as many as 9 distinct > items to keep in short-term memory. But bracketing some terms > as in `(x+1 > 0) and (y >= 5)` can reduce that down to as few > as two items. > (4) But too many parens obscure the meaning of the expression too. Aim > for a good balance, neither too few nor too many. Your judgement > of the right number of parens is a skill, which will come with > experience. (5) use APL -- all ordinary operators group right to left and at the same precedence level -- https://mail.python.org/mailman/listinfo/python-list
