Python in a Nutshell

Expressions and Operators

An expression is a phrase of code that the Python interpreter can evaluate to produce a value. The simplest expressions are literals and identifiers. You build other expressions by joining subexpressions with the operators and/or delimiters in Table 4-2. This table lists the operators in decreasing order of precedence, so operators with higher precedence are listed before those with lower precedence. Operators listed together have the same precedence. The A column lists the associativity of the operator, which can be L (left-to-right), R (right-to-left), or NA (non-associative).

In Table 4-2, expr, key, f, index, x, and y indicate any expression, while attr and arg indicate identifiers. The notation ,... indicates that commas join zero or more repetitions, except for string conversion, where one or more repetitions are allowed. A trailing comma is also allowed and innocuous in all such cases, except with string conversion, where it’s forbidden.

Table 4-2. Operator precedence in expressions

Operator	Description	A
`expr,...`	String conversion	NA
{key:expr,...}	Dictionary creation	NA
[expr,...]	List creation	NA
(expr,...)	Tuple creation or simple parentheses	NA
f(expr,...)	Function call	L
x[index:index]	Slicing	L
x[index]	Indexing	L
x.attr	Attribute reference	L
x**y	Exponentiation (x to yth power)	R
~x	Bitwise NOT	NA
+ x, - x	Unary plus and minus	NA
x * y, x / y, x // y, x % y