Iterating over lists in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print each fruit in the list.

Python

fruits = ['apple', 'banana', 'cherry']
for [1] in fruits:
    print([1])

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

Afruit

Bfruits

Citem

Dlist

Attempts:

3 left

💡 Hint

Common Mistakes

Using the list name instead of a variable for each element.

Using a reserved word like 'list' as a variable.

We use a variable name to represent each element in the list during the loop. Here, fruit is the variable that takes each value from fruits.

2fill in blank

medium

Complete the code to sum all numbers in the list.

Python

numbers = [1, 2, 3, 4]
total = 0
for num in numbers:
    total += [1]
print(total)

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

Anum

Bnumbers

Ctotal

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Adding the whole list instead of one number.

Using a variable that is not defined in the loop.

Inside the loop, num represents each number from the list. We add it to total to get the sum.

3fill in blank

hard

Fix the error in the loop to print each character in the word.

Python

word = 'hello'
for [1] in word:
    print(char)

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

Aword

Bstring

Cletter

Dchar

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different variable name in the loop and print.

Using the whole string as the loop variable.

The loop variable should be char because the print statement uses char. This way, each character is printed.

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

words = ['cat', 'house', 'tree', 'a', 'dog']
lengths = { [1]: [2]([1]) for [1] in words if len([1]) > 3 }

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

Aword

Blen

Clength

Dsize

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Using a non-existent function like length() or size().

We use word as the variable for each item in the list. The function len() gives the length of each word.

5fill in blank

hard

Fill all three blanks to create a dictionary with uppercase words as keys and their lengths as values for words longer than 2 letters.

Python

words = ['hi', 'hello', 'yes', 'no']
result = { [1]: [2] for [3] in words if len([3]) > 2 }

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

Aword.upper()

Blen(word)

Cword

Dword.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing variable names in the loop and dictionary.

Using lower() instead of upper() for keys.

word is the loop variable. We use word.upper() as the key and len(word) as the value in the dictionary.

Practice

1. What does the following code do?

for item in [1, 2, 3]:
    print(item)

easy

A. Prints the whole list once

B. Prints numbers 1 to 3 without spaces

C. Prints each number 1, 2, and 3 on a new line

D. Causes an error because of the loop

Solution

1. Step 1: Understand the for loop over a list

   The loop goes through each element in the list [1, 2, 3] one by one.

2. Step 2: Print each element during iteration

   Each element (1, then 2, then 3) is printed on its own line because of the print statement.

3. Final Answer:

   Prints each number 1, 2, and 3 on a new line -> Option C

4. Quick Check:

   Loop prints items one by one [OK]

Hint: For loops print each list item separately [OK]

Common Mistakes:

• Thinking it prints the whole list at once
• Expecting numbers to print on the same line
• Confusing loop variable with list itself

2. Which of these is the correct syntax to loop over a list named fruits?

easy

A. for fruit in fruits:
print(fruit)

B. for fruits in fruit:
print(fruits)

C. loop fruit in fruits:
print(fruit)

D. for fruit to fruits:
print(fruit)

Solution

1. Step 1: Identify correct for loop syntax

   The correct Python syntax uses 'for variable in list:' to loop over items.

2. Step 2: Check each option

   for fruit in fruits: print(fruit) uses 'for fruit in fruits:', which is correct. Others use invalid keywords or reversed names.

3. Final Answer:

   for fruit in fruits: print(fruit) -> Option A

4. Quick Check:

   Use 'for item in list:' syntax [OK]

Hint: Remember: for variable in list: [OK]

Common Mistakes:

• Swapping variable and list names
• Using wrong keywords like 'loop' or 'to'
• Missing colon after for statement

3. What is the output of this code?

numbers = [2, 4, 6]
sum = 0
for n in numbers:
    sum += n
print(sum)

medium

A. 12

B. 0

C. 246

D. Error

Solution

1. Step 1: Understand the loop adding numbers

   The loop adds each number in the list [2, 4, 6] to sum, starting from 0.

2. Step 2: Calculate the total sum

   sum = 0 + 2 + 4 + 6 = 12

3. Final Answer:

   12 -> Option A

4. Quick Check:

   Sum of list items = 12 [OK]

Hint: Add each item inside the loop to get total [OK]

Common Mistakes:

• Printing sum before loop
• Concatenating numbers as strings
• Forgetting to initialize sum to 0

4. Find the error in this code:

items = [10, 20, 30]
for i in items
    print(i)

medium

A. List name is incorrect

B. Wrong variable name in loop

C. Indentation error in print

D. Missing colon after for statement

Solution

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

   The for loop must end with a colon ':' to be valid syntax.

2. Step 2: Identify missing colon

   The code misses ':' after 'for i in items', causing a syntax error.

3. Final Answer:

   Missing colon after for statement -> Option D

4. Quick Check:

   For loops need ':' at end [OK]

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

Common Mistakes:

• Forgetting colon after for statement
• Using wrong variable names
• Incorrect indentation of print

5. You have a list of lists: data = [[1, 2], [3, 4], [5, 6]]. How do you print all numbers one by one using iteration?

hard

A. print(data[0][0], data[1][1], data[2][2])

B. for sublist in data:
for num in sublist:
print(num)

C. for i in range(len(data)):
print(data[i])

D. for num in data:
print(num)

Solution

1. Step 1: Understand nested lists and iteration

   Each item in data is a list itself, so we need two loops: one for each sublist, one for numbers inside.

2. Step 2: Use nested for loops to access all numbers

   The outer loop goes through each sublist, the inner loop prints each number inside that sublist.

3. Final Answer:

   for sublist in data: for num in sublist: print(num) -> Option B

4. Quick Check:

   Nested loops print all inner items [OK]

Hint: Use nested loops for lists inside lists [OK]

Common Mistakes:

• Trying to print sublists directly
• Using single loop only
• Accessing wrong indexes causing errors