Python Loops (for, while) Exercises

• In Python, a for loop uses the in keyword and usually works with an iterable (like a list, tuple, string, or range).
• The correct syntax is:

for variable in iterable:
    # loop body

• Option 2 is correct: for i in range(0,5) iterates from 0 to 4.
• Option 1 looks like C/Java syntax (not valid in Python).
• Option 3 uses incorrect to keyword (Python doesn’t have it).
• Option 4 uses foreach, which exists in other languages like PHP, but not in Python.

This tests whether learners can identify the basic correct syntax of a Python for loop.

• for loop: Commonly used when the number of iterations is known in advance (e.g., iterating over a list, range, or string).
• while loop: Used when we want to continue looping until a condition becomes false, and the number of iterations may not be known beforehand.
• Option 1 correctly explains the key difference.
• Option 2 is incorrect — speed depends on the task, not the loop type.
• Option 3 is incorrect — for loops work with any iterable, not just numbers.
• Option 4 is incorrect — they serve different purposes.

• The for loop iterates over each character in the string "Python".
• print(char, end=" ") prints each character followed by a space, instead of the default newline.
• Output:

P y t h o n 

• Option 1: Default print without end=" " would print each character on a new line.
• Option 2: Missing the trailing space after last character.
• Option 3: Incorrect grouping of characters.

This demonstrates iteration over strings and customizing print behavior using the end parameter.

• range(3) generates numbers starting from 0 up to 3 (exclusive).
• The for loop iterates over these values and prints them:

0
1
2

• Option 1: Starts at 1 incorrectly.
• Option 3: Includes 3, but range(3) stops before 3.
• Option 4: Prints in reverse order, which is not the case here.

This shows the zero-based indexing behavior of Python’s range() and simple for loop iteration.

• while loops are ideal when the number of iterations is not known beforehand and depends on a condition.

Example:

command = ""
while command != "exit":
    command = input("Enter command: ")
    print("You entered:", command)

• Option 1, 3, 4: Known number of iterations → better suited for a for loop.

This question emphasizes choosing the appropriate loop type based on the scenario.

• The break statement exits the loop immediately when the condition i == 3 is True.
• Iteration steps:
  • i = 0 → printed
  • i = 1 → printed
  • i = 2 → printed
  • i = 3 → break occurs, loop stops

• Output:

0
1
2

• Option 1: Ignores the break.
• Option 2: Prints only after 3 → incorrect behavior.
• Option 4: Includes 3, but loop exits before printing 3.

This demonstrates using break to stop a loop based on a condition.

• The continue statement skips the rest of the loop body for the current iteration if the condition is True.

• Iteration steps:

  • i = 0 → i % 2 == 0 → skip → not printed
  • i = 1 → condition False → printed
  • i = 2 → skip
  • i = 3 → printed
  • i = 4 → skip

• Output:
   

  1
  3
  

   

• Option 1: Prints even numbers → wrong
• Option 2: Includes 5 → range(5) stops at 4
• Option 3: Prints all numbers → ignores continue

This demonstrates using continue to selectively skip iterations in a loop.

• A nested loop occurs when a loop is placed inside another loop.
• Common use cases:
  • Printing patterns (stars, numbers)
  • Iterating over multi-dimensional data (like lists of lists or matrices)
• Example:

  for i in range(3):
      for j in range(2):
          print(i, j)
  

  Output:

  0 0
  0 1
  1 0
  1 1
  2 0
  2 1
  

• Option 1: Loop inside a function is not necessarily nested
• Option 2: Loops can run multiple times
• Option 4: Loops do not run in parallel by default in Python

Nested loops are important for complex iteration patterns and handling multi-level data structures.

• range(start, stop, step) generates numbers starting from start up to stop (exclusive), incrementing by step.
• Here: range(2, 10, 3) → numbers: 2, 5, 8
• Output:

  2 5 8
  

• Option 2: Prints all numbers 2–9 sequentially → ignores step
• Option 3: Starts from 0 → incorrect
• Option 4: 7 is included incorrectly → should be 8

 This demonstrates using step values in range() to control loop increments.

• The loop iterates over numbers from 1 to 5 (range(1,6) excludes 6).
• total += i adds each number to total:
  • 1 → total = 1
  • 2 → total = 3
  • 3 → total = 6
  • 4 → total = 10
  • 5 → total = 15
• Output: 15
• Option 2: Sum of 1–4 only → incorrect
• Option 3: Only last iteration’s value → incorrect
• Option 4: Sum over 1–6? → incorrect

This illustrates accumulating values using a loop.

• The outer loop (i) runs 1 to 3.
• The inner loop (j) also runs 1 to 3.
• i * j calculates multiplication for each pair (i,j).
• end=" " prints on the same line, and print() without arguments moves to the next line after each inner loop.

Step by step:

• i=1: 1*1=1, 1*2=2, 1*3=3 → 1 2 3
• i=2: 2*1=2, 2*2=4, 2*3=6 → 2 4 6
• i=3: 3*1=3, 3*2=6, 3*3=9 → 3 6 9
• Option 2: Adds numbers instead of multiplying → incorrect
• Option 3: Squares j only → incorrect
• Option 4: Prints all numbers in one line → ignores line break

This demonstrates nested loops for pattern generation or tabular output.

• This code finds the maximum number in a list using a for loop.

• Steps:

  • max_num = 3 (initial)
  • num = 3 → not greater → max_num = 3
  • num = 7 → greater → max_num = 7
  • num = 2 → not greater → max_num = 7
  • num = 9 → greater → max_num = 9
  • num = 4 → not greater → max_num = 9

• Output: 9

• Option 1,2,3: Do not consider the full comparison.

This illustrates finding the maximum value in a list using loops without built-in functions.

• The loop runs i from 1 to 5 (range(1, n+1) includes 5).
• "*" multiplied by i prints increasing stars each line, exactly 1 → 5 stars.
• Output:

*
**
***
****
*****

• Option 1: Prints decreasing stars → incorrect.
• Option 2: Prints 6 stars on the last line → incorrect, because the loop stops at i = 5.
• Option 4: Includes indentation → not in this code.

This demonstrates pattern printing using loops and string multiplication in Python.

• Outer loop: i takes values 2, 3, 4.
• Inner loop: j runs from 1 up to i-1.

Step-by-step:

• For i = 2: j = 1 → count = 0 + 1 = 1
• For i = 3: j = 1, 2 → count = 1 + 1 + 2 = 4
• For i = 4: j = 1, 2, 3 → count = 4 + 1 + 2 + 3 = 10

Final result printed = 10.

• Option 1: Too low (misses contributions).
• Option 2: Incorrect sum.
• Option 4: Higher than actual.
• Option 3: Correct.

This demonstrates nested loop accumulation logic.

• We want to start from 10 and print down to 1.
• Correct loop:
  • Initialize i = 10
  • Condition: while i >= 1
  • Decrement each step (i -= 1)

Why others are wrong:

• Option 1: Wrong condition (i < 1), loop never runs.
• Option 2: Increment instead of decrement → infinite loop.
• Option 3: Starts at 1 and decrements → also infinite loop.

Therefore, only Option 4 works correctly.

• The loop starts with i = 0.
• Each iteration: i is incremented first (i += 1).
• When i == 3, the continue statement skips the print, so 3 is not printed.
• Values printed: 1, 2, 4, 5.

Why others are wrong:

• Option 1: Incorrect, includes 3 (but 3 is skipped).
• Option 2: Starts with 0 (not possible, since i += 1 runs before print).
• Option 4: Starts at 2, misses earlier prints.

Thus, the correct tricky output is 1, 2, 4, 5.

• Outer loop: i goes from 1 to 5.
• if i % 2 == 0: continue → skips even numbers (2 and 4).
• Inner loop: prints i, repeated i times.
• Actual output:

  1 
  3 3 3 
  5 5 5 5 5
  

   

• Outer loop: i = 1, 2, 3.
• Inner loop: j = 1, 2, 3.
• If i == j, the inner loop breaks (stops for that i).

Step-by-step:

• i = 1: j = 1 → condition true → break immediately → nothing printed.
• i = 2: j = 1 → not equal → print 2 1 → j = 2 → equal → break.
• i = 3: j = 1 → not equal → print 3 1 → j = 2 → not equal → print 3 2 → j = 3 → equal → break.

Final output:

2 1
3 1
3 2

That matches Option 4.

• In Python, a for...else block runs the else part only if the loop is not terminated by break.
• Option 2:
• Loop runs from 0 → 4, printing all values.
• No break → else executes, printing "Done". 
• Option 1: Has a break at i == 2, so "Done" never prints.
• Option 3: Breaks at i == 4, so "Done" is skipped.
• Option 4: Always prints "Done", but not using for...else.

Thus, the correct snippet is Option 2.

• while i < 3: runs while i = 0 → 2.
• i += 1 increments i each iteration.
• When i == 2, break executes → loop exits immediately.
• The else block does NOT execute because loop was terminated with break.
• print(i) prints 2.

Step-by-step:

• i = 0 → i = 1 → not 2 → continue
• i = 1 → i = 2 → equals 2 → break → exit loop
• else skipped → print(i) → 2