Operator precedence and evaluation order in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is operator precedence in Python?

Operator precedence determines the order in which different operators in an expression are evaluated. Operators with higher precedence are evaluated before those with lower precedence.

beginner

Which operator has higher precedence: multiplication (*) or addition (+)?

Multiplication (*) has higher precedence than addition (+), so it is evaluated first in an expression without parentheses.

intermediate

What does evaluation order mean in Python expressions?

Evaluation order is the sequence in which parts of an expression are calculated. Even if operators have the same precedence, Python evaluates them from left to right (for most operators).

beginner

How do parentheses affect operator precedence and evaluation order?

Parentheses have the highest precedence. Expressions inside parentheses are evaluated first, overriding the normal precedence rules.

beginner

Consider the expression: 3 + 4 * 2. What is the result and why?

The result is 11 because multiplication (*) has higher precedence than addition (+). So, 4 * 2 is evaluated first (8), then 3 + 8 equals 11.

In the expression 5 + 3 * 2, which operation is performed first?

A Multiplication

B Addition

C Both at the same time

D Depends on the order written

Multiplication has higher precedence than addition, so 3 * 2 is done first.

What is the result of (5 + 3) * 2?

A 16

B 11

C 10

D 13

Parentheses are evaluated first: 5 + 3 = 8, then multiplied by 2 equals 16.

Which operator has the highest precedence in Python?

A Multiplication (*)

B Addition (+)

C Parentheses ()

D Exponentiation (**)

Parentheses have the highest precedence and force evaluation inside them first.

If two operators have the same precedence, how does Python decide which to evaluate first?

A Depends on the operator

B Randomly

C Right to left

D Left to right

Python evaluates operators with the same precedence from left to right, except for some like exponentiation.

What is the result of 2 ** 3 ** 2 in Python?

A 64

B 512

C 256

D 16

Exponentiation is right-associative, so 3 ** 2 = 9 first, then 2 ** 9 = 512.

Explain how operator precedence and evaluation order work together in Python expressions.

Think about how Python decides what to calculate first in a math expression.

Describe how parentheses change the way Python evaluates an expression.

Imagine grouping parts of a math problem to solve them first.

Practice

1. Which operator has the highest precedence in the expression 3 + 4 * 2?

easy

A. Multiplication (*)

B. Addition (+)

C. Subtraction (-)

D. Division (/)

Solution

1. Step 1: Recall operator precedence rules

   Multiplication (*) has higher precedence than addition (+), subtraction (-), and division (/).

2. Step 2: Identify highest precedence operator in expression

   In 3 + 4 * 2, multiplication (*) runs before addition (+).

3. Final Answer:

   Multiplication (*) -> Option A

4. Quick Check:

   Highest precedence = Multiplication (*) [OK]

Hint: Multiplication and division run before addition and subtraction [OK]

Common Mistakes:

• Thinking addition runs before multiplication
• Ignoring operator precedence
• Assuming left to right always applies

2. Which of the following expressions is syntactically correct in Python?

easy

A. 5 + * 3

B. 4 + (3 * 2)

C. 7 / / 2

D. 8 - -

Solution

1. Step 1: Check each expression for syntax errors

   5 + * 3 has two operators in a row without operand: invalid.
   4 + (3 * 2) uses parentheses correctly and valid operators.
   7 / / 2 has double division operator which is invalid.
   8 - - ends with operator without operand: invalid.

2. Step 2: Confirm correct syntax

   Only 4 + (3 * 2) is syntactically correct: 4 + (3 * 2).

3. Final Answer:

   4 + (3 * 2) -> Option B

4. Quick Check:

   Valid syntax = 4 + (3 * 2) [OK]

Hint: Check for missing operands or extra operators [OK]

Common Mistakes:

• Using two operators in a row
• Missing parentheses around expressions
• Ending expression with an operator

3. What is the output of the following code?

result = 10 - 3 * 2 + 4 // 2
print(result)

medium

A. 5

B. 8

C. 6

D. 4

Solution

1. Step 1: Apply operator precedence and evaluate multiplication and floor division first

   3 * 2 = 6
   4 // 2 = 2

2. Step 2: Evaluate the expression left to right with addition and subtraction

   10 - 6 + 2 = 4 + 2 = 6

3. Final Answer:

   6 -> Option C

4. Quick Check:

   10 - 6 + 2 = 6 [OK]

Hint: Multiply and divide before add and subtract [OK]

Common Mistakes:

• Adding before multiplying
• Using normal division instead of floor division
• Ignoring left to right evaluation for same precedence

4. Find the error in this expression:

value = 5 + (3 * 2

medium

A. No error, expression is correct

B. Wrong operator used

C. Extra operator before 2

D. Missing closing parenthesis

Solution

1. Step 1: Check parentheses balance

   Expression has an opening parenthesis '(' but no matching closing parenthesis ')'.

2. Step 2: Identify syntax error

   Missing closing parenthesis causes syntax error in Python.

3. Final Answer:

   Missing closing parenthesis -> Option D

4. Quick Check:

   Parentheses must be balanced [OK]

Hint: Count opening and closing parentheses carefully [OK]

Common Mistakes:

• Ignoring missing parentheses
• Assuming expression is valid without closing parenthesis
• Confusing operator errors with syntax errors

5. Given the expression result = (2 + 3) * (4 - 1) ** 2 // 5, what is the value of result?

hard

A. 9

B. 15

C. 5

D. 25

Solution

1. Step 1: Evaluate parentheses and exponentiation first

   (2 + 3) = 5
   (4 - 1) = 3
   3 ** 2 = 9

2. Step 2: Multiply and then floor divide

   5 * 9 = 45
   45 // 5 = 9

3. Final Answer:

   9 -> Option A

4. Quick Check:

   Parentheses and exponent first, then multiply, then floor divide [OK]

Hint: Do parentheses and powers before multiply/divide [OK]

Common Mistakes:

• Ignoring exponentiation precedence
• Dividing before multiplying
• Not applying floor division correctly