2.5: Order of operations
- Page ID
- 40854
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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)
is4
, and(1+1)**(5-2)
is8
. 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**3
is9
, not27
, and2 * 3**2
is18
, not36
. - Multiplication and Division have higher precedence than Addition and Subtraction. So
2*3-1
is5
, not4
, and6+4/2
is8
, not5
. - 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 bypi
. To divide by \(2 \pi \), you can use parentheses or writedegrees / 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.