Understanding Python Operator Precedence and Evaluation Order, Lecture notes of Advanced Computer Programming

Download Understanding Python Operator Precedence and Evaluation Order and more Lecture notes Advanced Computer Programming in PDF only on Docsity!

Python Operator Precedence and

Associativity

Riya Jacob K

Assistant Professor on Contract

Dept of Computer Applications

How does the operator precedence

work in Python?

• 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 simpleSee a simple exampleexample givengiven below.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.

Operator precedence table in Python

Give examples of associativity in

Python

• 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:Result: 11

  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 the examples below.

• Checking right-left associativity of ** exponent

  operator

Output: 256

print(4print(4 ** 2 **** 2 ** 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).

Give examples of

nonassociative operators

• 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.
• • ## SetSet thethe valuesvalues ofof a,a, b,b, cc x = 11, y = 12, z = 13

Expression is incorrect

Non-associative operators

Error -> SyntaxError: invalid syntax

x = y += 12