When an expression contains more than one operator, the order of evaluation depends on the order of operations. For mathematical operators, Python follows mathematical convention. The acronym PEMDAS is a useful way to remember the rules:
- Parentheses have the highest precedence and can be used to force an expression to evaluate in the order you want. Since expressions in parentheses are evaluated first,
2 * (3-1)is
8. You can also use parentheses to make an expression easier to read, as in
(minute * 100) / 60, even if it doesn’t change the result.
- Exponentiation has the next highest precedence, so
1 + 2**3is
2 * 3**2is
- Multiplication and Division have higher precedence than Addition and Subtraction. So
- Operators with the same precedence are evaluated from left to right (except exponentiation). So in the expression
degrees / 2 * pi, the division happens first and the result is multiplied by
pi. To divide by \(2 \pi \), you can use parentheses or write
degrees / 2 / pi.
I don’t work very hard to remember the precedence of operators. If I can’t tell by looking at the expression, I use parentheses to make it obvious.