On Wed, Aug 10, 2011 at 3:37 PM, Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> wrote: >> Without the parentheses, this is legal but (probably) useless; it >> applies the unary + operator to the return value of those functions. >> Putting the + at the end of the previous line at least prevents that, >> since most unary operators bind to the operand on the right; > > Not so: > >>>> x = (42 + - > ... 100) >>>> >>>> x > -58
Your unary - is binding to the operand to its right, in this case the 100. (I think I have left and right correct; being in theatre has a tendency to make you forget which is which.) Your + is binary, operating on 42 and the result of applying unary - to 100, which is -100. My point about binding can be illustrated by inventing an operator @. Let's say that a@b is the atan2 of a and b, and x@ is x factorial (I can't imagine what deranged mind would do something like this, apart from my own). y = 5 @ # 120, as per factorial x = 5 @ 2 # 1.19 or so, as per atan2 foo(123) # Calls foo() and discards its return value z = 5 @ foo(123) Is that last example one statement or two? But this situation shouldn't ever occur in Python, because all its unary operators (not, -, +, ~) bind to the operand to their right (I don't think there's any I've missed, are there?). It does mean, however, that a leading operator is not unambiguous. Without the surrounding parentheses and/or otherwise-unexpected indentation, an expression beginning with a + could conceivably be applying the unary plus operator to the rest of the expression, rather than implying that it's continuing the previous line. Chris Angelico -- http://mail.python.org/mailman/listinfo/python-list
