Operator precedence problem

[Marko Rauhamaa]

Random832 <random832 at fastmail.com>:

> Sure, it's obvious to _me_ that << and >> have higher precedence than &
> and |, and that "and" has a higher precedence than "or", but can I
> assume the other people know this?

No need to assume. Just read the spec:

   lambda         Lambda expression
   if – else      Conditional expression
   or             Boolean OR
   and            Boolean AND
   not x          Boolean NOT
   in, not in, is, is not, <, <=, >, >=, !=, ==
                  Comparisons, including membership tests and identity
                  tests
   |              Bitwise OR
   ^              Bitwise XOR
   &              Bitwise AND
   <<, >>         Shifts
   +, -           Addition and subtraction
   *, @, /, //, % Multiplication, matrix multiplication division,
                  remainder [5]
   +x, -x, ~x     Positive, negative, bitwise NOT
   **             Exponentiation [6]
   await x        Await expression
   x[index], x[index:index], x(arguments...), x.attribute
                  Subscription, slicing, call, attribute reference
   (expressions...), [expressions...], {key: value...}, {expressions...}
                  Binding or tuple display, list display, dictionary
                  display, set display

   <URL: https://docs.python.org/3/reference/expressions.html#operat
   or-precedence>

> [To keep this on-topic, let's assume that this discussion has a goal of
> getting something along the lines of "always/sometimes/never use
> "unnecessary" parentheses" into PEP7/PEP8. Speaking of, did you know
> that C has lower precedence for the bitwise operators &^| than for
> comparisons? That was something that tripped me up for a very long time
> and undermined my confidence as to other aspects of the bitwise
> operators]

Yes, I happened to know that. Python's the same way.

However, no need to memorize. It's all there in the spec. Same as with
stdlib functions. Keep checking the spec.

You *can* assume other people have read the spec. Even more importantly,
you can assume the Python interpreter complies with the spec.


Marko