Logical operators in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the and operator do in Python?

The and operator returns True only if both conditions on its sides are True. Otherwise, it returns False.

beginner

What is the result of True or False in Python?

The result is True because the or operator returns True if at least one condition is True.

beginner

Explain the not operator in Python.

The not operator reverses the value of a condition. If the condition is True, not makes it False, and vice versa.

beginner

What will False and True return?

It will return False because and needs both sides to be True to return True.

beginner

How do logical operators help in decision making in code?

Logical operators combine multiple conditions to decide if a block of code should run. They help check if one or more conditions are true or false.

What does the expression True and False evaluate to?

A True

B None

C Error

D False

The and operator returns True only if both sides are True. Here, one side is False, so the result is False.

Which operator returns True if at least one condition is true?

A or

B not

C xor

D and

The or operator returns True if any one or both conditions are True.

What is the result of not True?

A True

B None

C False

D Error

The not operator reverses the value. So not True is False.

Which logical operator would you use to check if two conditions are both true?

A and

B or

C not

D xor

The and operator checks if both conditions are true.

What does False or False evaluate to?

A True

B False

C None

D Error

The or operator returns True if at least one side is true. Here both are false, so result is False.

Explain how the and, or, and not operators work in Python with simple examples.

Think about how these operators combine or reverse true/false values.

Describe a real-life situation where you might use logical operators in a program.

Consider checking multiple conditions before doing something, like checking weather and time before going outside.

Practice

1. Which logical operator in Python returns True only if both conditions are true?

easy

A. or

B. xor

C. not

D. and

Solution

1. Step 1: Understand the meaning of logical operators

   The and operator returns True only if both conditions are true.

2. Step 2: Compare with other operators

   or returns True if any condition is true, not reverses a condition, and xor is not a Python keyword.

3. Final Answer:

   and -> Option D

4. Quick Check:

   Both true conditions = and [OK]

Hint: Use 'and' when all conditions must be true [OK]

Common Mistakes:

• Confusing 'and' with 'or'
• Thinking 'not' combines conditions
• Using 'xor' which is not a Python keyword

2. Which of the following is the correct syntax to check if x is NOT equal to 10 using logical operators?

easy

A. not x = 10

B. not (x == 10)

C. x != 10

D. x not= 10

Solution

1. Step 1: Understand how to negate a condition

   The not operator reverses a condition. To check if x is not equal to 10, negate x == 10.

2. Step 2: Check syntax correctness

   not (x == 10) is correct syntax. x != 10 is also correct but not using logical operators explicitly. Other options have syntax errors.

3. Final Answer:

   not (x == 10) -> Option B

4. Quick Check:

   Use 'not' with parentheses for negation [OK]

Hint: Use 'not (condition)' to reverse it properly [OK]

Common Mistakes:

• Writing 'not x = 10' (invalid syntax)
• Using 'x not= 10' (invalid operator)
• Confusing '!=' with 'not' operator usage

3. What is the output of the following code?

print((5 > 3) and (2 == 2) or not (4 < 1))

medium

A. True

B. False

C. SyntaxError

D. None

Solution

1. Step 1: Evaluate each condition

   5 > 3 is True, 2 == 2 is True, 4 < 1 is False.

2. Step 2: Apply logical operators step-by-step

   (5 > 3) and (2 == 2) is True and True = True.
   Then not (4 < 1) is not False = True.
   Finally, True or True = True.

3. Final Answer:

   True -> Option A

4. Quick Check:

   True and True or True = True [OK]

Hint: Evaluate 'and' before 'or', then apply 'not' [OK]

Common Mistakes:

• Ignoring operator precedence
• Misinterpreting 'not' effect
• Assuming 'or' has higher priority than 'and'

4. Find the error in this code snippet:

if not x > 10 and < 5:
    print("Valid")

medium

A. Syntax error due to incomplete condition after 'and'

B. Incorrect use of 'not' operator

C. Missing parentheses around conditions

D. No error, code runs fine

Solution

1. Step 1: Analyze the condition after 'and'

   The condition after and is just < 5, which is incomplete because it lacks a variable to compare.

2. Step 2: Identify syntax error

   Python expects a full condition after and. This causes a syntax error.

3. Final Answer:

   Syntax error due to incomplete condition after 'and' -> Option A

4. Quick Check:

   Conditions must be complete after logical operators [OK]

Hint: Check each condition is complete after 'and' or 'or' [OK]

Common Mistakes:

• Assuming 'not' applies to both conditions
• Ignoring incomplete condition after 'and'
• Missing variable in second condition

5. You want to check if a number n is between 10 and 20 (inclusive) or exactly 0. Which condition correctly uses logical operators?

hard

A. not (n < 10 or n > 20) and n == 0

B. n >= 10 and (n <= 20 or n == 0)

C. (n >= 10 and n <= 20) or n == 0

D. n >= 10 or n <= 20 and n == 0

Solution

1. Step 1: Understand the condition requirements

   The number n should be between 10 and 20 inclusive, or exactly 0.

2. Step 2: Analyze each option

   (n >= 10 and n <= 20) or n == 0 correctly groups the range check with and and then uses or for the zero check.
   n >= 10 and (n <= 20 or n == 0) changes the logic, allowing n == 0 to be combined incorrectly.
   n >= 10 or n <= 20 and n == 0 mixes operators without parentheses, causing wrong logic.
   not (n < 10 or n > 20) and n == 0 incorrectly requires n to be zero and in the range simultaneously.

3. Final Answer:

   (n >= 10 and n <= 20) or n == 0 -> Option C

4. Quick Check:

   Range check with 'and', zero check with 'or' [OK]

Hint: Group range with 'and', combine with 'or' for zero [OK]

Common Mistakes:

• Wrong operator precedence
• Misplacing parentheses
• Combining conditions incorrectly