Python operators precedence rules

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Precedence Rules

The order in which operators are evaluated in an expression is known as precedence rules.

Precedence rules for arithmetic, relational and logical operators:

Operator/Convention	Description	Explanation
( )	Items within parentheses are evaluated first	In (a * (b + c)) - d, the + is evaluated first, then *, then -.
* / % + -	Arithmetic operators (using their precedence rules)	z - 45 * y < 53 evaluates * first, then -, then <.
< <= > >= == !=	Relational, (in)equality, and membership operators	x < 2 or x >= 10 is evaluated as (x < 2) or (x >= 10) because < and >= have precedence over or.
not	not (logical NOT)	not x or y is evaluated as (not x) or y
and	Logical AND	x == 5 or y == 10 and z != 10 is evaluated as (x == 5) or ((y == 10) and (z != 10)) because and has precedence over or.
or	Logical OR	x == 7 or x < 2 is evaluated as (x == 7) or (x < 2) because < and == have precedence over or

Best Practices

A common error is to write an expression that is evaluated in a different order than expected. Good practice is to use parentheses in expressions to make the intended order of evaluation explicit.

For example, a programmer might write:

not x + y < 5 intending (not x) + y < 5, but the interpreter computes not ((x + y) < 5) because the addition operator + has the highest precedence and is computed first, followed by the relational operation <, and finally the logical not operation.