Iteration using range() in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of range() with step

What is the output of this Python code?

result = []
for i in range(2, 10, 3):
    result.append(i)
print(result)

Python

result = []
for i in range(2, 10, 3):
    result.append(i)
print(result)

A [2, 6, 9]

B [2, 5, 8]

C [2, 3, 4, 5, 6, 7, 8, 9]

D [3, 6, 9]

💡 Hint

Remember that range(start, stop, step) includes start but excludes stop.

range(2, 10, 3) starts at 2 and adds 3 each time until it reaches or passes 10. So it produces 2, 5, 8.

❓ Predict Output

intermediate

Counting iterations with negative step

What will be printed by this code?

count = 0
for x in range(10, 0, -2):
    count += 1
print(count)

Python

count = 0
for x in range(10, 0, -2):
    count += 1
print(count)

A 5

B 6

C 0

D 4

💡 Hint

Count how many numbers are generated from 10 down to 1 stepping by -2.

range(10, 0, -2) generates 10, 8, 6, 4, 2. That's 5 numbers, so count is 5.

🧠 Conceptual

advanced

Behavior of range() with equal start and stop

What does list(range(5, 5)) produce in Python?

A Raises ValueError

B [5]

C [0, 1, 2, 3, 4]

D []

💡 Hint

Think about whether the stop value is included or excluded.

range(start, stop) includes start but excludes stop. If start == stop, no numbers are generated.

❓ Predict Output

advanced

Output of nested loops with range()

What is the output of this code?

result = []
for i in range(1, 4):
    for j in range(i):
        result.append(j)
print(result)

Python

result = []
for i in range(1, 4):
    for j in range(i):
        result.append(j)
print(result)

A [0, 1, 0, 1, 2]

B [1, 2, 3]

C [0, 0, 1, 0, 1, 2]

D [0, 1, 2]

💡 Hint

Look at how many times the inner loop runs for each outer loop iteration.

For i=1, j runs 0; for i=2, j runs 0,1; for i=3, j runs 0,1,2. All appended in order.

🔧 Debug

expert

Identify the error in this range usage

What error does this code raise?

for i in range(5, 1, 1):
    print(i)

Python

for i in range(5, 1, 1):
    print(i)

A Prints nothing

B Prints 5, 6, 7, 8, 9

C Raises ValueError

D Infinite loop

💡 Hint

Check if the step direction matches the start and stop values.

range(5, 1, 1) tries to count up from 5 to 1 but 1 is less than 5, so no values are generated.

Practice

1. What does range(5) do in a Python for loop?

easy

A. Generates numbers from 0 to 4

B. Generates numbers from 1 to 5

C. Generates numbers from 0 to 5

D. Generates numbers from 1 to 4

Solution

1. Step 1: Understand the range function

   range(5) starts at 0 by default and stops before 5.

2. Step 2: Identify the numbers generated

   The numbers generated are 0, 1, 2, 3, 4.

3. Final Answer:

   Generates numbers from 0 to 4 -> Option A

4. Quick Check:

   range(5) = 0,1,2,3,4 [OK]

Hint: Remember range stops before the end number [OK]

Common Mistakes:

• Thinking range(5) includes 5
• Starting count at 1 by default
• Confusing stop value as inclusive

2. Which of the following is the correct syntax to loop 3 times using range()?

easy

A. for i in range(1, 3):

B. for i in range(3):

C. for i in range(0, 3, 2):

D. for i in range(3, 0):

Solution

1. Step 1: Check each range syntax

   for i in range(1, 3): loops from 1 to 2 (2 times), for i in range(3): loops 0 to 2 (3 times), for i in range(0, 3, 2): loops 0 and 2 (2 times), for i in range(3, 0): runs zero times because start > stop without negative step.

2. Step 2: Identify the correct loop count

   Only for i in range(3): loops exactly 3 times: 0,1,2.

3. Final Answer:

   for i in range(3): -> Option B

4. Quick Check:

   range(3) loops 3 times [OK]

Hint: range(n) loops exactly n times starting at 0 [OK]

Common Mistakes:

• Using range(1, 3) which loops 2 times
• Using invalid range with start > stop
• Confusing step parameter

3. What is the output of this code?

for i in range(2, 7, 2):
    print(i, end=' ')

medium

A. 0 2 4 6

B. 2 3 4 5 6

C. 2 4 6 8

D. 2 4 6

Solution

1. Step 1: Understand the range parameters

   range(2, 7, 2) starts at 2, stops before 7, stepping by 2.

2. Step 2: List the numbers generated

   Numbers are 2, 4, 6.

3. Final Answer:

   2 4 6 -> Option D

4. Quick Check:

   range(2,7,2) = 2,4,6 [OK]

Hint: Start, stop, step control numbers generated [OK]

Common Mistakes:

• Including 7 in output
• Using wrong step size
• Starting from 0 instead of 2

4. Find the error in this code:

for i in range(5, 1):
    print(i)

medium

A. No error, prints 5 to 1

B. SyntaxError due to wrong range syntax

C. Loop does not run because start > stop without step

D. Infinite loop

Solution

1. Step 1: Analyze the range parameters

   range(5, 1) means start at 5, stop before 1, with default step 1.

2. Step 2: Understand loop behavior

   Since start is greater than stop and step is positive, the loop runs zero times.

3. Final Answer:

   Loop does not run because start > stop without step -> Option C

4. Quick Check:

   range(5,1) empty range [OK]

Hint: Positive step needs start < stop to run [OK]

Common Mistakes:

• Expecting loop to run backwards
• Thinking syntax error occurs
• Assuming infinite loop

5. You want to print all odd numbers from 1 to 15 using range(). Which code does this correctly?

hard

A. for i in range(1, 16, 2): print(i)

B. for i in range(0, 15, 2): print(i)

C. for i in range(1, 15): if i % 2 == 1: print(i)

D. for i in range(1, 16): print(i % 2)

Solution

1. Step 1: Identify odd numbers range

   Odd numbers from 1 to 15 are 1,3,5,...,15.

2. Step 2: Check each option

   for i in range(1, 16, 2): print(i) uses range(1,16,2) which generates 1,3,5,...,15 directly. for i in range(0, 15, 2): print(i) starts at 0 (even). for i in range(1, 15): if i % 2 == 1: print(i) misses 15 (range(1,15) goes to 14) and uses extra if check. for i in range(1, 16): print(i % 2) prints 1 or 0, not numbers.

3. Final Answer:

   for i in range(1, 16, 2): print(i) -> Option A

4. Quick Check:

   range(1,16,2) = odd numbers [OK]

Hint: Use step=2 starting at 1 for odd numbers [OK]

Common Mistakes:

• Starting at 0 for odd numbers
• Forgetting to include last number
• Printing modulo instead of number