List concatenation and repetition in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to concatenate two lists.

Python

result = [1, 2, 3] [1] [4, 5, 6]

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

A+

B*

C/

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' instead of '+' causes an error or unexpected behavior.

Using '-' or '/' are not valid for lists.

The + operator joins two lists together.

2fill in blank

medium

Complete the code to repeat the list three times.

Python

result = [0, 1] [1] 3

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

A-

B+

C/

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' concatenates lists but does not repeat.

Using '-' or '/' are not valid for lists.

The * operator repeats the list multiple times.

3fill in blank

hard

Fix the error in the code to correctly concatenate two lists.

Python

result = [1, 2, 3] [1] [4]

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

A-

B*

C+

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to add a list and an integer directly causes an error.

Using '*' with a number on the right repeats the list, but here the right side is not a list.

To concatenate lists, both sides must be lists. Here, 4 is not a list, so use + with a list on the right side.

4fill in blank

hard

Fill both blanks to create a list of three repetitions of [7, 8] concatenated with [9].

Python

result = [7, 8] [1] 3 [2] [9]

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

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' before '*' changes the order of operations.

Using '-' or '/' causes errors.

First, repeat the list [7, 8] three times using *, then concatenate the result with [9] using +.

5fill in blank

hard

Fill all three blanks to create a list with the uppercase letters repeated twice and concatenated with ['Z'].

Python

letters = ['a', 'b', 'c']
result = [[1] for l in letters] [2] 2 [3] ['Z']

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

Al.upper()

B*

C+

Dl.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Using l.lower() instead of l.upper().

Using '+' instead of '*' for repetition.

Using '*' instead of '+' for concatenation.

Use l.upper() to convert letters to uppercase, repeat the list twice with *, then concatenate with + ['Z'].

Practice

1. What does the expression [1, 2] + [3, 4] do in Python?

easy

A. Creates a new list combining both lists: [1, 2, 3, 4]

B. Repeats the first list twice: [1, 2, 1, 2]

C. Creates a list of two lists: [[1, 2], [3, 4]]

D. Raises a TypeError because lists cannot be added

Solution

1. Step 1: Understand the + operator with lists

   The + operator joins two lists into one new list containing all elements from both.

2. Step 2: Apply + to [1, 2] and [3, 4]

   Joining these lists results in [1, 2, 3, 4].

3. Final Answer:

   Creates a new list combining both lists: [1, 2, 3, 4] -> Option A

4. Quick Check:

   List concatenation = combined list [OK]

Hint: Use + to join lists, not to repeat [OK]

Common Mistakes:

• Thinking + repeats lists instead of joining
• Confusing list concatenation with nesting
• Expecting an error when adding lists

2. Which of the following is the correct syntax to repeat the list [5, 6] three times?

easy

A. [5, 6] ** 3

B. [5, 6] + 3

C. 3 + [5, 6]

D. [5, 6] * 3

Solution

1. Step 1: Identify the operator for repetition

   The * operator repeats a list multiple times when used with an integer.

2. Step 2: Check syntax correctness

   [5, 6] * 3 repeats the list three times: [5, 6, 5, 6, 5, 6].

3. Final Answer:

   [5, 6] * 3 -> Option D

4. Quick Check:

   List repetition uses * operator [OK]

Hint: Use * with list and number to repeat [OK]

Common Mistakes:

• Using + instead of * for repetition
• Trying to use ** which is invalid for lists
• Confusing order of operands for repetition

3. What is the output of this code?

lst1 = [1]
lst2 = [2, 3]
result = lst1 * 2 + lst2 * 3
print(result)

medium

A. [1, 1, 2, 3, 2, 3, 2, 3]

B. [1, 2, 3, 1, 2, 3]

C. [1, 1, 2, 3, 3, 3]

D. [1, 1, 2, 3, 2, 3]

Solution

1. Step 1: Calculate lst1 * 2

   Repeating [1] twice gives [1, 1].

2. Step 2: Calculate lst2 * 3

   Repeating [2, 3] three times gives [2, 3, 2, 3, 2, 3].

3. Step 3: Concatenate the two results

   Adding [1, 1] + [2, 3, 2, 3, 2, 3] results in [1, 1, 2, 3, 2, 3, 2, 3].

4. Final Answer:

   [1, 1, 2, 3, 2, 3, 2, 3] -> Option A

5. Quick Check:

   Repeat then join lists = combined repeated list [OK]

Hint: Repeat lists first, then add them [OK]

Common Mistakes:

• Adding before repeating
• Miscounting repeated elements
• Confusing order of concatenation

4. Find the error in this code snippet:

list_a = [1, 2]
list_b = [3, 4]
result = list_a * list_b
print(result)

medium

A. No error, prints [1, 2, 3, 4]

B. SyntaxError due to missing parentheses

C. TypeError because * expects an integer, not a list

D. ValueError because lists cannot be multiplied

Solution

1. Step 1: Understand list repetition rules

   List repetition uses * with an integer, not another list.

2. Step 2: Identify the error in list_a * list_b

   Multiplying two lists causes a TypeError because the right operand must be int.

3. Final Answer:

   TypeError because * expects an integer, not a list -> Option C

4. Quick Check:

   List * list is invalid, needs int [OK]

Hint: Right side of * must be integer for list repetition [OK]

Common Mistakes:

• Trying to multiply two lists directly
• Expecting concatenation with * operator
• Confusing syntax error with type error

5. You have two lists:
fruits = ['apple', 'banana']
veggies = ['carrot']
How do you create a new list that repeats the fruits twice and veggies three times, then combines them all in order?

hard

A. fruits * veggies * 5

B. fruits * 2 + veggies * 3

C. fruits + veggies * 5

D. (fruits + veggies) * 5

Solution

1. Step 1: Repeat fruits and veggies separately

   fruits * 2 repeats fruits twice; veggies * 3 repeats veggies three times.

2. Step 2: Concatenate the repeated lists

   Adding these repeated lists combines them in order as desired.

3. Final Answer:

   fruits * 2 + veggies * 3 -> Option B

4. Quick Check:

   Repeat separately then add lists [OK]

Hint: Repeat lists separately, then add [OK]

Common Mistakes:

• Repeating combined list instead of separate lists
• Using invalid multiplication of lists
• Confusing order of operations