Precedence and Associativity of Operators in Python
When dealing with operators in Python we have to know about the concept of Python operator precedence and associativity as these determine the priorities of the operator otherwise, we’ll see unexpected outputs.
Operator Precedence: This is used in an expression with more than one operator with different precedence to determine which operation to perform first.
Example: Solve
10 + 20 * 30
10 + 20 * 30 is calculated as 10 + (20 * 30) and not as (10 + 20) * 30
Code:
Python3
# Precedence of '+' & '*'expr = 10 + 20 * 30 print(expr) |
Output:
610
Example: Now, let’s see an example on logical ‘or‘ & logical ‘and‘ operator. ‘if‘ block is executed even if the age is 0. Because precedence of logical ‘or‘ is greater than the logical ‘and‘.
Python3
# Precedence of 'or' & 'and'name = "Alex"age = 0 if name == "Alex" or name == "John" and age >= 2 : print("Hello! Welcome.")else : print("Good Bye!!") |
Output:
Hello! Welcome.
Hence, To run the ‘else‘ block we can use parenthesis( ) as their precedence is highest among all the operators.
Python3
# Precedence of 'or' & 'and'name = "Alex"age = 0 if ( name == "Alex" or name == "John" ) and age >= 2 : print("Hello! Welcome.")else : print("Good Bye!!") |
Output:
Good Bye!!
Operator Associativity: If an expression contains two or more operators with the same precedence then Operator Associativity is used to determine. It can either be Left to Right or from Right to Left.
Example: ‘*’ and ‘/’ have the same precedence and their associativity is Left to Right, so the expression “100 / 10 * 10” is treated as “(100 / 10) * 10”.
Code:
Python3
# Left-right associativity# 100 / 10 * 10 is calculated as # (100 / 10) * 10 and not # as 100 / (10 * 10)print(100 / 10 * 10) # Left-right associativity# 5 - 2 + 3 is calculated as # (5 - 2) + 3 and not # as 5 - (2 + 3)print(5 - 2 + 3) # left-right associativityprint(5 - (2 + 3)) # right-left associativity# 2 ** 3 ** 2 is calculated as # 2 ** (3 ** 2) and not # as (2 ** 3) ** 2print(2 ** 3 ** 2) |
Output:
100 6 0 512
Operators Precedence and Associativity are two main characteristics of operators that determine the evaluation order of sub-expressions in absence of brackets.
Example: Solve
100 + 200 / 10 - 3 * 10
100 + 200 / 10 - 3 * 10 is calculated as 100 + (200 / 10) - (3 * 10) and not as (100 + 200) / (10 - 3) * 10
Code:
Python3
expression = 100 + 200 / 10 - 3 * 10print(expression ) |
Output:
90.0
Please see the following precedence and associativity table for reference. This table lists all operators from the highest precedence to the lowest precedence. is, is not in, not in Identity Membership operatorsOperator Description Associativity ( ) Parentheses left-to-right ** Exponent right-to-left * / % Multiplication/division/modulus left-to-right + – Addition/subtraction left-to-right << >> Bitwise shift left, Bitwise shift right left-to-right < <=
> >=Relational less than/less than or equal to
Relational greater than/greater than or equal toleft-to-right == != Relational is equal to/is not equal to left-to-right left-to-right & Bitwise AND left-to-right ^ Bitwise exclusive OR left-to-right | Bitwise inclusive OR left-to-right not Logical NOT right-to-left and Logical AND left-to-right or Logical OR left-to-right =
+= -=
*= /=
%= &=
^= |=
<<= >>=Assignment
Addition/subtraction assignment
Multiplication/division assignment
Modulus/bitwise AND assignment
Bitwise exclusive/inclusive OR assignment
Bitwise shift left/right assignmentright-to-left
Attention geek! Strengthen your foundations with the Python Programming Foundation Course and learn the basics.
To begin with, your interview preparations Enhance your Data Structures concepts with the Python DS Course. And to begin with your Machine Learning Journey, join the Machine Learning – Basic Level Course
