2.7: Order of Operations
- Page ID
- 2996
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When more than one operator appears in an expression, the order of evaluation depends on the rules of precedence. 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 4, and(1+1)**(5-2)
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
2**1+1
is 3, not 4, and3*1**3
is 3, not 27. - Multiplication and Division have the same precedence, which is higher than Addition and Subtraction, which also have the same precedence. So
2*3-1
is 5, not 4, and6+4/2
is 8.0, not 5. - Operators with the same precedence are evaluated from left to right. So the expression
5-3-1
is 1, not 3, because the5-3
happens first and then1
is subtracted from2
.
When in doubt, always put parentheses in your expressions to make sure the computations are performed in the order you intend.