sorted() function in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the sorted() function do in Python?

The sorted() function takes any iterable (like a list or tuple) and returns a new list with all the items in ascending order by default.

beginner

How do you sort a list in descending order using sorted()?

Use the reverse=True argument inside sorted(). For example: sorted(my_list, reverse=True) sorts the list from highest to lowest.

intermediate

What is the difference between sorted() and the list method sort()?

sorted() returns a new sorted list and works on any iterable. list.sort() changes the original list in place and returns None.

intermediate

How can you sort a list of strings ignoring case using sorted()?

Use the key=str.lower argument to sort strings without case sensitivity. Example: sorted(words, key=str.lower).

beginner

What type of object does sorted() return?

sorted() always returns a new list, even if the input is a tuple or other iterable.

What will sorted([3, 1, 2]) return?

A [1, 2, 3]

B [3, 2, 1]

C [3, 1, 2]

D Error

sorted() returns a new list sorted in ascending order.

Which argument sorts a list in descending order?

A reverse=True

B descending=True

C order='desc'

D desc=True

The correct argument is reverse=True.

What does sorted() return when given a tuple?

A A sorted tuple

B A sorted list

C The original tuple

D An error

sorted() always returns a new list, even if input is a tuple.

How do you sort strings ignoring case?

A sorted(strings, key=ignore_case)

B sorted(strings, ignore_case=True)

C sorted(strings, key=str.lower)

D sorted(strings, case=False)

Use key=str.lower to ignore case while sorting.

Which is true about list.sort() compared to sorted()?

A <code>list.sort()</code> returns a tuple

B <code>list.sort()</code> returns a new sorted list

C <code>list.sort()</code> works on any iterable

D <code>list.sort()</code> sorts the list in place

list.sort() changes the original list and returns None.

Explain how to use the sorted() function to sort a list in descending order and ignoring case for strings.

Think about the arguments <code>reverse</code> and <code>key</code>.

Describe the difference between sorted() and list.sort() in Python.

Consider what happens to the original list.

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