Guide to Python Operator Precedence and Associativity

In this tutorial, you’ll learn about Python operator precedence and associativity. This topic is crucial for programmers to understand the semantics of Python operators.

After reading it, you should be able to know how Python evaluates the order of its operators. Some operators have higher precedence than others such as the multiplication operator has higher priority than the addition operator, so do multiplication before addition.

In an expression, Python interpreter evaluates operators with higher precedence first. And, except the exponent operator (**) all other operators get evaluated from left to right.

Table of Content.

Python Operator Precedence and Associativity

Python Operator Precedence and Associativity

Python operator precedence

When we group a set of values, variables, operators or function calls that turn out as an expression. And once you execute that expression, Python interpreter evaluates it as a valid expression.

See a simple example given below.

>>> 3 + 4
7

Here, the ‘3 +4’ is a Python expression. It contains one operator and two operands. However, a more complex statement can include multiple operators.

To evaluate complex expressions, Python lays out the rule of precedence. It governs the order in which the operations take place.

See the below example which combines multiple operators to form a compound expression.

# Multiplication get evaluated before
# the addition operation
# Result: 17
5 + 4 * 3

However, it is possible to alter the evaluation order with the help of parentheses (). It can override the precedence of the arithmetic operators.

# Parentheses () overriding the precedence of the arithmetic operators
# Output: 27
(5 + 4) * 3

Refer the below table which lists the operators with the highest precedence at the top and lowest at the bottom.

Operators
Usage
{ }
Parentheses (grouping)
f(args…)
Function call
x[index:index]
Slicing
x[index]
Subscription
x.attribute
Attribute reference
**
Exponent
~x
Bitwise not
+x, -x
Positive, negative
*, /, %
Product, division, remainder
+, –
Addition, subtraction
<<, >>
Shifts left/right
&
Bitwise AND
^
Bitwise XOR
|
Bitwise OR
in, not in, is, is not, <, <=, >, >=,
<>, !=, ==
Comparisons, membership, identity
not x
Boolean NOT
and
Boolean AND
or
Boolean OR
lambda
Lambda expression

Python operator associativity

In the above table, you can confirm that some of the groups have many operators. It means that all operators in a group are at the same precedence level.

And whenever two or more operators have the same precedence, then associativity defines the order of operations.

Hence, associativity is the order in which Python evaluates an expression containing multiple operators of the same precedence. Almost all operators except the exponent (**) support the left-to-right associativity.

For example, the product (*) and the modulus (%) have the same precedence. So, if both appear in an expression, then the left one will get evaluated first.

# Testing Left-right associativity
# Result: 1
print(4 * 7 % 3)

# Testing left-right associativity
# Result: 0
print(2 * (10 % 5))

As said earlier, the only operator which has right-to-left associativity in Python is the exponent (**) operator.

See example below.

# Checking right-left associativity of ** exponent operator
# Output: 256
print(4 ** 2 ** 2)

# Checking the right-left associativity
# of **
# Output: 256
print((4 ** 2) ** 2)

You might have observed that the ‘print(4 ** 2 ** 2)’ is similar to ‘(4 ** 2 ** 2).

Nonassociative operators

Python does have some operators such as assignment operators and comparison operators which don’t support associativity. Instead, there are special rules for the ordering of this type of operator which can’t be managed via associativity.

For example, the expression 5 < 7 < 9 does not mean (5 < 7) < 9 or 5 < (7 < 9). Also, the statement 5 < 7 < 9 is same as 5 < 7 and 7 < 9, and gets evaluated from left-to-right.

Moreover, chaining of assignments operators like a = b = c is perfectly alright whereas the ‘a = b += c’ will result in an error.

# Set the values of a, b, c
x = 11, y = 12, z = 13

# Expression is incorrect
# Non-associative operators
# Error -> SyntaxError: invalid syntax

x = y += 12

Now, you might like to check out how Python deals with operator precedence and associativity.

Quick wrap up – Python operator precedence

This tutorial did cover a very important topic – Python operator precedence and associativity. So, it should now be easier for you to create compound/complex expressions in Python.

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TechBeamers