sorted() function in Python

Introduction

The sorted() function helps you put items in order, like sorting names alphabetically or numbers from smallest to largest.

When you want to arrange a list of names in alphabetical order.

When you need to sort numbers from lowest to highest.

When you want to organize data before showing it to users.

When you want to sort items without changing the original list.

When you want to sort based on a special rule, like sorting by length of words.

Syntax

Python

sorted(iterable, *, key=None, reverse=False)

iterable can be any group of items like a list, tuple, or string.

key lets you choose a rule for sorting, like sorting by length.

Examples

Sorts numbers from smallest to largest.

Python

sorted([3, 1, 2])

Sorts words in reverse alphabetical order.

Python

sorted(['apple', 'banana', 'cherry'], reverse=True)

Sorts words by their length, shortest first.

Python

sorted(['apple', 'banana', 'cherry'], key=len)

Sorts letters in the word alphabetically.

Python

sorted('hello')

Sample Program

This program shows how sorted() keeps the original list the same and creates a new sorted list. It also shows sorting numbers in reverse order.

Python

fruits = ['banana', 'apple', 'cherry']
sorted_fruits = sorted(fruits)
print('Original list:', fruits)
print('Sorted list:', sorted_fruits)

numbers = [5, 2, 9, 1]
sorted_numbers = sorted(numbers, reverse=True)
print('Numbers sorted from largest to smallest:', sorted_numbers)

Important Notes

sorted() does not change the original list; it makes a new sorted list.

You can sort any iterable, not just lists.

Use reverse=True to sort backwards.

Summary

sorted() arranges items in order and returns a new list.

You can sort by normal order, reverse, or a custom rule with key.

The original data stays the same after sorting.

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