sorted() function in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of sorting a list of tuples by the second element?

Consider the following Python code that sorts a list of tuples by the second item in each tuple.

Python

data = [(3, 4), (1, 2), (5, 1)]
sorted_data = sorted(data, key=lambda x: x[1])
print(sorted_data)

A [(5, 1), (1, 2), (3, 4)]

B [(1, 2), (3, 4), (5, 1)]

C [(3, 4), (1, 2), (5, 1)]

D [(5, 1), (3, 4), (1, 2)]

💡 Hint

Look at the second element of each tuple and sort by that.

The sorted() function sorts the list by the key function, which here returns the second element of each tuple. So the tuples are ordered by 1, 2, then 4.

❓ Predict Output

intermediate

What is the output when sorting a string with sorted()?

What will be printed by this code?

Python

result = sorted('banana')
print(result)

A ['a', 'a', 'a', 'b', 'n', 'n']

B ['b', 'a', 'n', 'a', 'n', 'a']

C ['n', 'n', 'b', 'a', 'a', 'a']

D ['a', 'b', 'n']

💡 Hint

sorted() returns a list of characters sorted alphabetically.

The string 'banana' is split into characters and sorted alphabetically, resulting in three 'a's, one 'b', and two 'n's in order.

❓ Predict Output

advanced

What is the output of sorting a dictionary by its values?

Given this dictionary, what will be the output of the sorted() call?

Python

scores = {'Alice': 88, 'Bob': 75, 'Charlie': 90}
sorted_scores = sorted(scores.items(), key=lambda item: item[1])
print(sorted_scores)

A [('Alice', 88), ('Bob', 75), ('Charlie', 90)]

B [('Bob', 75), ('Charlie', 90), ('Alice', 88)]

C [('Charlie', 90), ('Alice', 88), ('Bob', 75)]

D [('Bob', 75), ('Alice', 88), ('Charlie', 90)]

💡 Hint

The key function sorts by the dictionary values.

sorted() sorts the items by the second element of each tuple (the score), so the order is Bob (75), Alice (88), Charlie (90).

❓ Predict Output

advanced

What is the output of sorting a list with reverse=True?

What will this code print?

Python

numbers = [4, 1, 7, 3]
sorted_numbers = sorted(numbers, reverse=True)
print(sorted_numbers)

A [4, 1, 7, 3]

B [1, 3, 4, 7]

C [7, 4, 3, 1]

D [7, 3, 4, 1]

💡 Hint

reverse=True sorts from largest to smallest.

The sorted() function sorts the list in descending order because reverse=True is set.

🧠 Conceptual

expert

Which option will cause a TypeError when used with sorted()?

Which of these options will cause a TypeError when passed as the key argument to sorted()?

A key=lambda x: x[0]

B key=5

C key=str.lower

D key=lambda x: len(x)

💡 Hint

The key argument must be a function, not a number.

Passing an integer (5) as the key argument causes a TypeError because sorted() expects a callable function for key.

Practice

1. What does the sorted() function do in Python?

easy

A. Returns a new list with items arranged in order

B. Changes the original list to be sorted

C. Deletes all items from the list

D. Returns the largest item in the list

Solution

1. Step 1: Understand the purpose of sorted()

   The sorted() function creates a new list with the elements arranged in ascending order by default.

2. Step 2: Compare with other options

   It does not change the original list, nor does it delete items or return just the largest item.

3. Final Answer:

   Returns a new list with items arranged in order -> Option A

4. Quick Check:

   sorted() returns new sorted list [OK]

Hint: Remember: sorted() returns a new list, original stays same [OK]

Common Mistakes:

• Thinking sorted() changes the original list
• Confusing sorted() with max() or min()
• Assuming sorted() deletes items

2. Which of the following is the correct syntax to sort a list nums in reverse order using sorted()?

easy

A. sorted(nums, reverse=False)

B. sorted(nums, reverse=0)

C. sorted(nums, reverse=false)

D. sorted(nums, reverse=True)

Solution

1. Step 1: Check the correct parameter for reverse sorting

   The sorted() function uses the keyword argument reverse=True to sort in descending order.

2. Step 2: Validate the parameter type

   The value must be the boolean True, not False, numbers like 0, or undefined names.

3. Final Answer:

   sorted(nums, reverse=True) -> Option D

4. Quick Check:

   Use reverse=True (boolean) for descending sort [OK]

Hint: Use reverse=True (boolean), not False/0/undefined [OK]

Common Mistakes:

• Using reverse=False (sorts ascending)
• Passing falsy numbers like 0
• Using undefined lowercase 'false'

3. What is the output of the following code?

words = ['pear', 'apple', 'orange']
sorted_words = sorted(words, key=len)
print(sorted_words)

medium

A. ['pear', 'apple', 'orange']

B. ['pear', 'apple', 'orange'] sorted by length

C. ['apple', 'orange', 'pear']

D. ['pear', 'apple', 'orange'] sorted by length ascending

Solution

1. Step 1: Understand the key parameter

   The key=len tells sorted() to sort the list by the length of each word.

2. Step 2: Sort words by length

   Lengths: 'pear' (4), 'apple' (5), 'orange' (6). Sorted ascending by length: ['pear', 'apple', 'orange'].

3. Final Answer:

   ['pear', 'apple', 'orange'] -> Option A

4. Quick Check:

   sorted(words, key=len) sorts by length ascending [OK]

Hint: key=len sorts items by their length ascending [OK]

Common Mistakes:

• Confusing sorting by value vs length
• Assuming sorted() changes original list
• Misreading the order of output

4. Find the error in this code snippet:

numbers = [3, 1, 4, 1, 5]
sorted_numbers = sorted(numbers, key='abs')
print(sorted_numbers)

medium

A. sorted() cannot sort numbers

B. Missing parentheses after sorted

C. key argument should be a function, not a string

D. reverse argument is required

Solution

1. Step 1: Check the key argument type

   The key parameter must be a function, like abs, not a string.

2. Step 2: Identify the error

   Here, key='abs' is a string, which causes a TypeError.

3. Final Answer:

   key argument should be a function, not a string -> Option C

4. Quick Check:

   key needs a function, not string [OK]

Hint: Pass function to key, not string name [OK]

Common Mistakes:

• Passing string instead of function to key
• Thinking sorted() can't sort numbers
• Forgetting parentheses in function calls

5. You have a list of tuples representing people and their ages:

people = [('Alice', 30), ('Bob', 25), ('Charlie', 35), ('David', 25)]

How do you use sorted() to sort this list by age ascending, and if ages are equal, by name alphabetically?

hard

A. sorted(people, key=lambda x: (x[0], x[1]))

B. sorted(people, key=lambda x: (x[1], x[0]))

C. sorted(people, key=lambda x: x[1])

D. sorted(people, key=lambda x: x[0])

Solution

1. Step 1: Understand sorting by multiple criteria

   To sort by age first, then by name if ages tie, use a tuple key with age first, then name.

2. Step 2: Write the key function

   The lambda lambda x: (x[1], x[0]) returns a tuple (age, name) for sorting.

3. Step 3: Check other options

   The option sorting by name then age is incorrect. Options sorting by only one field are wrong.

4. Final Answer:

   sorted(people, key=lambda x: (x[1], x[0])) -> Option B

5. Quick Check:

   Use tuple key (age, name) for multi-level sort [OK]

Hint: Use tuple in key: (age, name) for multi-level sorting [OK]

Common Mistakes:

• Sorting by name before age
• Using single key instead of tuple
• Confusing tuple order in key function