Nested conditional execution in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is nested conditional execution in Python?

Nested conditional execution means putting one if-else statement inside another if or else block. It helps check multiple conditions step-by-step.

beginner

How do you write a nested if statement in Python?

You write an if statement inside another if or else block, like:

if condition1:
    if condition2:
        # code here

beginner

Why use nested conditional execution?

It helps check detailed conditions in order. For example, first check if a person is adult, then check if they have a driving license.

beginner

What happens if the outer condition in nested if is False?

The inner if statements are skipped completely because the outer condition controls if the inner code runs.

beginner

Example: What will this code print?

age = 20
if age >= 18:
    if age >= 21:
        print('Adult and can drink')
    else:
        print('Adult but cannot drink')
else:
    print('Not an adult')

It will print: Adult but cannot drink because age is 20, which is >= 18 but less than 21.

What does nested conditional execution allow you to do?

A Run code without any condition

B Write only one condition

C Skip all conditions

D Check multiple conditions inside each other

Nested conditional execution lets you check one condition inside another to handle complex decisions.

In nested if statements, when does the inner if run?

A Only if the outer if condition is True

B Always, no matter what

C Only if the outer if condition is False

D Never

The inner if runs only if the outer if condition is True, because it is inside that block.

What will this code print?

score = 85
if score >= 90:
    print('A grade')
else:
    if score >= 80:
        print('B grade')
    else:
        print('C grade')

A A grade

B B grade

C C grade

D No output

Score is 85, so outer if is False, inner if is True, so it prints 'B grade'.

Which keyword is NOT used in nested conditional execution?

A for

B else

C elif

D if

'for' is a loop keyword, not used for conditional execution.

What is the main benefit of using nested conditionals?

A Avoid using else statements

B Make code run faster

C Simplify checking multiple related conditions stepwise

D Write fewer lines of code

Nested conditionals help check related conditions one after another clearly.

Explain nested conditional execution and give a simple example.

Think about checking one condition inside another.

Describe how the flow of execution works in nested if statements.

Imagine opening boxes inside boxes only if the first box is open.

Practice

1. What does nested conditional execution mean in Python?

easy

A. An if or else inside another if or else

B. Using multiple if statements one after another

C. Writing if statements without indentation

D. Using only one if statement in a program

Solution

1. Step 1: Understand the meaning of nested conditionals

   Nested conditionals mean putting one conditional inside another, like an if inside an if.

2. Step 2: Compare options to definition

   An if or else inside another if or else correctly describes this as an if or else inside another if or else. Other options describe different or incorrect ideas.

3. Final Answer:

   An if or else inside another if or else -> Option A

4. Quick Check:

   Nested conditional = if inside if [OK]

Hint: Look for conditionals inside other conditionals [OK]

Common Mistakes:

• Thinking multiple separate ifs are nested
• Ignoring indentation importance
• Confusing nested with chained conditionals

2. Which of the following is the correct syntax for nested conditionals in Python?

easy

A. if x > 0:
if x < 10:
print('x is between 1 and 9')

B. if x > 0
if x < 10:
print('x is between 1 and 9')

C. if x > 0:
if x < 10:
print('x is between 1 and 9')

D. if x > 0:
print('x is positive')
else if x < 10:
print('x is less than 10')

Solution

1. Step 1: Check indentation and colons

   Python requires colons after if and proper indentation for nested blocks.

2. Step 2: Analyze each option

   if x > 0: if x < 10: print('x is between 1 and 9') uses colons and indents the inner if correctly. Options A and B miss colons or indentation. if x > 0: print('x is positive') else if x < 10: print('x is less than 10') uses invalid else if instead of elif.

3. Final Answer:

   if x > 0: if x < 10: print('x is between 1 and 9') -> Option C

4. Quick Check:

   Colons + indentation = correct syntax [OK]

Hint: Check colons and indentation for nested blocks [OK]

Common Mistakes:

• Missing colons after if statements
• Incorrect indentation of nested if
• Using else if instead of elif

3. What is the output of this code?

score = 85
if score >= 90:
    print('Grade A')
else:
    if score >= 80:
        print('Grade B')
    else:
        print('Grade C')

medium

A. Grade A

B. Grade B

C. Grade C

D. No output

Solution

1. Step 1: Check first condition

   score is 85, which is not >= 90, so skip first print.

2. Step 2: Check nested else condition

   Inside else, check if score >= 80. 85 >= 80 is True, so print 'Grade B'.

3. Final Answer:

   Grade B -> Option B

4. Quick Check:

   85 >= 80 triggers nested if [OK]

Hint: Follow conditions step-by-step inside else [OK]

Common Mistakes:

• Assuming first if is true for 85
• Ignoring nested else block
• Confusing indentation levels

4. Find the error in this nested conditional code:

num = 5
if num > 0:
if num < 10:
print('Number is between 1 and 9')

medium

A. Missing colon after first if

B. No error, code is correct

C. Using print without parentheses

D. Incorrect indentation of inner if and print

Solution

1. Step 1: Check colons

   Both if statements have colons, so no missing colon error.

2. Step 2: Check indentation

   Inner if and print are not indented under outer if, causing syntax error.

3. Final Answer:

   Incorrect indentation of inner if and print -> Option D

4. Quick Check:

   Nested blocks must be indented [OK]

Hint: Indent nested if and its code properly [OK]

Common Mistakes:

• Forgetting to indent nested blocks
• Confusing missing colon with indentation error
• Assuming print syntax error without checking Python version

5. You want to check if a number is positive, and if positive, check if it is even or odd. Which nested conditional code correctly prints 'Positive even' or 'Positive odd' accordingly?

hard

A. if num > 0:
if num % 2 == 0:
print('Positive even')
else:
print('Positive odd')

B. if num > 0 and num % 2 == 0:
print('Positive even')
else:
print('Positive odd')

C. if num > 0:
if num % 2 == 0:
print('Positive even')
else:
print('Positive odd')

D. if num > 0:
if num % 2 == 0:
print('Positive even')
else:
print('Positive odd')

Solution

1. Step 1: Understand the logic needed

   First check if number is positive, then inside that check if even or odd.

2. Step 2: Analyze options for correct nesting and indentation

   if num > 0: if num % 2 == 0: print('Positive even') else: print('Positive odd') correctly nests the even/odd check inside the positive check with proper indentation. if num > 0 and num % 2 == 0: print('Positive even') else: print('Positive odd') combines conditions but does not handle odd positive numbers correctly. Options C and D have indentation errors.

3. Final Answer:

   if num > 0: if num % 2 == 0: print('Positive even') else: print('Positive odd') -> Option A

4. Quick Check:

   Nested if with correct indentation prints right message [OK]

Hint: Indent inner if inside outer if for stepwise checks [OK]

Common Mistakes:

• Combining conditions incorrectly
• Indentation errors in nested blocks
• Missing else for odd case