Sorting and reversing lists in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to sort the list in ascending order.

Python

numbers = [5, 3, 8, 1]
numbers.[1]()
print(numbers)

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

Apop

Breverse

Cappend

Dsort

Attempts:

3 left

💡 Hint

Common Mistakes

Using reverse() instead of sort(), which only flips the list order.

Using append() or pop(), which add or remove items instead of sorting.

The sort() method arranges the list items in ascending order.

2fill in blank

medium

Complete the code to reverse the order of the list.

Python

letters = ['a', 'b', 'c', 'd']
letters.[1]()
print(letters)

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

Areverse

Bpop

Csort

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using sort() which arranges items but does not reverse the current order.

Using pop() or insert() which modify list items but do not reverse.

The reverse() method flips the order of the list items.

3fill in blank

hard

Fix the error in the code to sort the list in descending order.

Python

scores = [70, 85, 90, 60]
scores.sort([1]=True)
print(scores)

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

Areverse=True

Bdescending

Creverse

Dreverse_order

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect argument names like 'descending' or 'reverse_order'.

Putting the whole argument 'reverse=True' as the blank instead of just the argument name.

The sort() method uses the reverse=True argument to sort descending. The blank should be the argument name reverse.

4fill in blank

hard

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

Python

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

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

Alen(word)

B<=

C>

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong comparison operator like '<=' which selects shorter words.

Using 'word' instead of 'len(word)' for the dictionary values.

The dictionary comprehension uses len(word) to get the length and filters words with length greater than 3 using >.

5fill in blank

hard

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

Python

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

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

Aw.upper()

Blen(w)

C>

Dw.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase words as keys instead of uppercase.

Using wrong comparison operator like '<='.

Using the word itself as value instead of its length.

The dictionary comprehension uses w.upper() as keys, len(w) as values, and filters words longer than 2 with >.

Practice

1. What does the list.sort() method do to a list in Python?

easy

A. It arranges the list items in ascending order.

B. It reverses the order of the list items.

C. It removes duplicate items from the list.

D. It creates a new sorted list without changing the original.

Solution

1. Step 1: Understand the purpose of list.sort()

   The list.sort() method changes the original list to arrange its items in ascending order.

2. Step 2: Differentiate from other list methods

   Unlike list.reverse(), which flips the list order, list.sort() orders items from smallest to largest.

3. Final Answer:

   It arranges the list items in ascending order. -> Option A

4. Quick Check:

   list.sort() = ascending order [OK]

Hint: Remember: sort() orders ascending by default [OK]

Common Mistakes:

• Confusing sort() with reverse()
• Thinking sort() returns a new list
• Assuming sort() removes duplicates

2. Which of the following is the correct syntax to sort a list named numbers in descending order?

easy

A. numbers.sort(reverse=True)

B. numbers.sort(reverse=1)

C. numbers.sort(descending=True)

D. numbers.reverse(sort=True)

Solution

1. Step 1: Identify correct parameter for descending sort

   The sort() method accepts reverse=True to sort in descending order.

2. Step 2: Check syntax correctness

   numbers.sort(reverse=True) uses the correct syntax: numbers.sort(reverse=True). Other options use invalid parameters or method calls.

3. Final Answer:

   numbers.sort(reverse=True) -> Option A

4. Quick Check:

   sort(reverse=True) = descending order [OK]

Hint: Use reverse=True inside sort() for descending order [OK]

Common Mistakes:

• Using reverse=1 instead of reverse=True
• Using non-existent parameters like descending=True
• Calling reverse() with parameters

3. What is the output of the following code?

items = [3, 1, 4, 2]
items.sort()
items.reverse()
print(items)

medium

A. [1, 2, 3, 4]

B. [3, 1, 4, 2]

C. [4, 3, 2, 1]

D. [2, 3, 1, 4]

Solution

1. Step 1: Apply items.sort()

   This sorts the list in ascending order: [1, 2, 3, 4].

2. Step 2: Apply items.reverse()

   This reverses the sorted list, resulting in [4, 3, 2, 1].

3. Final Answer:

   [4, 3, 2, 1] -> Option C

4. Quick Check:

   sort() then reverse() = descending list [OK]

Hint: sort() then reverse() = descending order [OK]

Common Mistakes:

• Thinking reverse() sorts the list
• Assuming print shows original list
• Confusing order of method calls

4. The following code is intended to sort the list data in descending order. What is wrong?

data = [5, 2, 9, 1]
data.reverse()
data.sort()
print(data)

medium

A. The code will cause a syntax error.

B. The reverse() call should come after sort().

C. The sort() method does not exist for lists.

D. The list is already sorted, so no change happens.

Solution

1. Step 1: Analyze method order

   The code reverses the list first, then sorts it ascending, which cancels the reverse effect.

2. Step 2: Correct method order for descending sort

   To get descending order, first sort ascending, then reverse the list.

3. Final Answer:

   The reverse() call should come after sort(). -> Option B

4. Quick Check:

   sort() then reverse() = descending order [OK]

Hint: Sort first, then reverse for descending order [OK]

Common Mistakes:

• Reversing before sorting cancels sorting effect
• Thinking reverse() sorts the list
• Assuming method order does not matter

5. You have a list of words: words = ['apple', 'banana', 'cherry', 'date']. You want to sort them in reverse alphabetical order without changing the original list. Which code snippet achieves this?

hard

A. sorted_words = words.sort(reverse=True)

B. words.sort(reverse=True)

C. words.reverse(); words.sort()

D. sorted_words = sorted(words, reverse=True)

Solution

1. Step 1: Understand difference between sort() and sorted()

   sort() changes the original list; sorted() returns a new sorted list.

2. Step 2: Choose method that sorts in reverse without changing original

   Using sorted(words, reverse=True) returns a new list sorted in reverse alphabetical order, leaving words unchanged.

3. Final Answer:

   sorted_words = sorted(words, reverse=True) -> Option D

4. Quick Check:

   sorted() returns new sorted list [OK]

Hint: Use sorted() to keep original list unchanged [OK]

Common Mistakes:

• Using sort() which changes original list
• Chaining reverse() before sort() incorrectly
• Assigning sort() result which is None