For loop execution model in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print each number from 1 to 3.

Python

for num in [1]:
    print(num)

Drag options to blanks, or click blank then click option'

Arange(1, 4)

B[1, 2]

Clist(3)

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using a single number instead of a range.

Using a list with fewer numbers than needed.

The range(1, 4) function generates numbers 1, 2, and 3. The for loop prints each number.

2fill in blank

medium

Complete the code to sum all numbers from 1 to 5 using a for loop.

Python

total = 0
for i in range(1, 6):
    total += [1]
print(total)

Drag options to blanks, or click blank then click option'

Atotal

Bi

Crange(1, 6)

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Adding the total to itself instead of the loop variable.

Using the range function inside the loop body.

Inside the loop, we add the current number i to total to get the sum.

3fill in blank

hard

Fix the error in the code to print each character in the string.

Python

word = "hello"
for [1] in word:
    print(letter)

Drag options to blanks, or click blank then click option'

Achar

Bword

Cletter

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different variable name in the loop header and body.

Using the string variable name as the loop variable.

The loop variable should be letter because it is used inside the loop to print each character.

4fill in blank

hard

Fill both blanks to create a dictionary with words as keys and their lengths as values for words longer than 3 letters.

Python

lengths = { [1]: [2] for word in words if len(word) > 3 }

Drag options to blanks, or click blank then click option'

Aword

Blen(word)

Cword.upper()

Dlen

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method like word.upper() as the key.

Using the function len without calling it.

The dictionary keys are the words themselves, and the values are their lengths using len(word).

5fill in blank

hard

Fill all three blanks to create a dictionary with uppercase words as keys, their lengths as values, only for words longer than 4 letters.

Python

result = { [1]: [2] for word in words if [3] }

Drag options to blanks, or click blank then click option'

Aword.upper()

Blen(word)

Clen(word) > 4

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using the original word as key instead of uppercase.

Forgetting to call len(word) in the condition.

Using wrong comparison operators.

The keys are uppercase words using word.upper(), values are their lengths, and the condition filters words longer than 4 letters.

Practice

1. What does a for loop do in Python?

easy

A. Repeats a block of code for each item in a sequence

B. Runs code only once

C. Stops the program immediately

D. Creates a new variable

Solution

1. Step 1: Understand the purpose of a for loop

   A for loop runs code repeatedly for each item in a list, string, or range. 'Repeats a block of code for each item in a sequence' matches this; others do not.

2. Final Answer:

   Repeats a block of code for each item in a sequence -> Option A

3. Quick Check:

   For loop = repeat for each item [OK]

Hint: For loops repeat actions for every item in a list [OK]

Common Mistakes:

• Thinking for loops run only once
• Confusing for loops with if statements
• Believing for loops stop the program

2. Which of the following is the correct syntax for a for loop in Python?

easy

A. for (i=0; i<5; i++) print(i)

B. for i to range(5) print(i)

C. for i in range(5): print(i)

D. foreach i in range(5): print(i)

Solution

1. Step 1: Recall Python for loop syntax

   Python uses 'for variable in sequence:' followed by indented code. 'for i in range(5): print(i)' matches; others use wrong keywords or styles.

2. Final Answer:

   for i in range(5): print(i) -> Option C

3. Quick Check:

   Python for loop = for variable in sequence: [OK]

Hint: Use 'for variable in sequence:' syntax in Python [OK]

Common Mistakes:

• Using 'to' instead of 'in'
• Using C-style for loop syntax
• Using 'foreach' which is not Python

3. What is the output of this code?

for i in range(3):
    print(i * 2)

medium

A. 2 4 6

B. 0 1 2

C. 1 2 3

D. 0 2 4

Solution

1. Step 1: Trace the loop range and output

   range(3) gives i=0,1,2. Prints i*2: 0, 2, 4.

2. Final Answer:

   0 2 4 -> Option D

3. Quick Check:

   Multiply each i by 2 = 0 2 4 [OK]

Hint: Multiply loop variable by 2 for each iteration [OK]

Common Mistakes:

• Printing i instead of i*2
• Starting count from 1 instead of 0
• Confusing range(3) with range(1,3)

4. Find the error in this code:

for i in range(5)
    print(i)

medium

A. Indentation error on print line

B. Missing colon ':' after range(5)

C. range(5) is invalid syntax

D. Variable i is not defined

Solution

1. Step 1: Check for syntax errors in for loop

   Python requires ':' after the for statement. The code misses ':' after range(5).

2. Final Answer:

   Missing colon ':' after range(5) -> Option B

3. Quick Check:

   For loop needs ':' after header [OK]

Hint: Always add ':' after for loop header [OK]

Common Mistakes:

• Forgetting colon ':' after for statement
• Incorrect indentation
• Assuming range(5) is invalid

5. You want to create a list of squares for numbers 0 to 4 using a for loop. Which code correctly does this?

hard

A. squares = []
for i in range(5):
squares.append(i*i)
print(squares)

B. squares = [i*i for i in range(5)]
print(squares)

C. squares = []
for i in range(5):
squares = i*i
print(squares)

D. for i in range(5):
squares.append(i*i)
print(squares)

Solution

1. Step 1: Identify correct code for list of squares using for loop

   Initialize squares = [], then for i in range(5): append i*i, then print. squares = [] for i in range(5): squares.append(i*i) print(squares) works; others miss init, use comp, or overwrite.

2. Final Answer:

   squares = []\nfor i in range(5):\n squares.append(i*i)\nprint(squares) -> Option A

3. Quick Check:

   Initialize list, append squares in loop [OK]

Hint: Initialize list before loop, append inside loop [OK]

Common Mistakes:

• Not initializing list before appending
• Overwriting list variable inside loop
• Using list comprehension but question asks for for loop