Precedence and associativity of arithmetic operators in python

Output

Lunch being delivered

This program runs if block even when money is 0. It does not give us the desired output since the precedence of and is higher than or.

We can get the desired output by using parenthesis [] in the following way:

# Precedence of or & and
meal = "fruit"

money = 0

if [meal == "fruit" or meal == "sandwich"] and money >= 2:
    print["Lunch being delivered"]
else:
    print["Can't deliver lunch"]

Output

Can't deliver lunch

Associativity of Python Operators

We can see in the above table that more than one operator exists in the same group. These operators have the same precedence.

When two operators have the same precedence, associativity helps to determine the order of operations.

Associativity is the order in which an expression is evaluated that has multiple operators of the same precedence. Almost all the operators have left-to-right associativity.

For example, multiplication and floor division have the same precedence. Hence, if both of them are present in an expression, the left one is evaluated first.

# Left-right associativity
# Output: 3
print[5 * 2 // 3]

# Shows left-right associativity
# Output: 0
print[5 * [2 // 3]]

Output

3
0

Note: Exponent operator ** has right-to-left associativity in Python.

# Shows the right-left associativity of **
# Output: 512, Since 2**[3**2] = 2**9
print[2 ** 3 ** 2]

# If 2 needs to be exponated fisrt, need to use []
# Output: 64
print[[2 ** 3] ** 2]

We can see that 2 ** 3 ** 2 is equivalent to 2 ** [3 ** 2].

Non associative operators

Some operators like assignment operators and comparison operators do not have associativity in Python. There are separate rules for sequences of this kind of operator and cannot be expressed as associativity.

For example, x < y < z neither means [x < y] < z nor x < [y < z]. x < y < z is equivalent to x < y and y < z, and is evaluated from left-to-right.

Furthermore, while chaining of assignments like x = y = z = 1 is perfectly valid, x = y = z+= 2 will result in error.

# Initialize x, y, z
x = y = z = 1

# Expression is invalid
# [Non-associative operators]
# SyntaxError: invalid syntax

x = y = z+= 2

Output

  File "", line 8
    x = y = z+= 2
             ^
SyntaxError: invalid syntax

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What is precedence of operators in Python?

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