Logical operators in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of combined logical operators

What is the output of this code snippet?

Python

a = True
b = False
c = True
result = a and b or c
print(result)

A False

B None

C SyntaxError

D True

💡 Hint

Remember that 'and' has higher precedence than 'or'.

The expression evaluates as (a and b) or c. Since a and b is False, the result is c which is True.

❓ Predict Output

intermediate

Result of chained logical expressions

What will be printed by this code?

Python

x = 5
print((x > 3) and (x < 10) or (x == 5))

A False

B True

C None

D TypeError

💡 Hint

Check each comparison and how 'and' and 'or' combine them.

x > 3 is True, x < 10 is True, so (True and True) is True. True or (x == 5) is True.

❓ Predict Output

advanced

Output of logical operators with non-boolean values

What is the output of this code?

Python

result = '' or 0 and 'Hello' or None
print(result)

A Hello

B ''

C 0

D None

💡 Hint

Remember that 'and' has higher precedence than 'or' and that logical operators return the last evaluated operand.

The expression evaluates as: '' or (0 and 'Hello') or None. 0 and 'Hello' evaluates to 0 because 'and' returns the first falsy value or last value. Then '' or 0 evaluates to 0 (since '' is falsy). Finally, 0 or None evaluates to None if 0 is falsy, but since 0 is falsy, the last 'or None' returns None. However, in Python, 'or' returns the first truthy value or the last value if none are truthy. Here, '' is falsy, 0 is falsy, so '' or 0 returns 0, then 0 or None returns None. But since 0 is falsy, the final result is None. Actually, the correct evaluation is: '' or (0 and 'Hello') or None -> '' or 0 or None -> 0 or None -> None. So the output is None.

❓ Predict Output

advanced

Output of complex logical expression with parentheses

What does this code print?

Python

a = False
b = True
c = False
print((a or b) and (b or c))

A True

B None

C False

D SyntaxError

💡 Hint

Evaluate inside parentheses first, then combine with 'and'.

(a or b) is True, (b or c) is True, so True and True is True.

❓ Predict Output

expert

Value of variable after logical operations with assignment

What is the value of variable 'x' after running this code?

Python

x = None
x = x or []
x.append(1)
x = x and [2, 3]
x.append(4)
print(x)

A [2, 3, 4]

B [1, 4]

C None

D AttributeError

💡 Hint

Track how 'x' changes after each line and how logical operators affect assignment.

Initially x is None, then x = x or [] sets x to []. Then x.append(1) makes x = [1]. Then x = x and [2, 3] sets x to [2, 3] because x is truthy. Then x.append(4) adds 4 to the list, so x = [2, 3, 4].

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