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Python sorted() Function

The sorted() method sorts the items of any iterable.

note
danger

You can not sort a list that contains BOTH string values AND numeric values.

Syntax​

sorted(iterable, key, reverse)

sorted() Parameters​

Python sorted() function parameters:

ParameterConditionDescription
iterableRequiredAny iterable (list, tuple, string, dictionary, set etc.) to sort.
keyOptionalA function to specify the sorting criteria. Default value is None.
reverseOptionalSetting it to True sorts the list in reverse order. Default value is False.

sorted() Return Value​

Python sorted() function returns a new sorted list from the items in iterable.

Examples​

Example 1: Sort a String​

sorted() function sorts strings alphabetically:

my_string = "Tutorial Reference!"
sorted_string = sorted(my_string)
print(sorted_string)  # Output: [' ', '!', 'R', 'T', 'a', 'c', 'e', 'e', 'e', 'e', 'f', 'i', 'l', 'n', 'o', 'r', 'r', 't', 'u']

output

[' ', '!', 'R', 'T', 'a', 'c', 'e', 'e', 'e', 'e', 'f', 'i', 'l', 'n', 'o', 'r', 'r', 't', 'u']

Example 2: Sort a List​

sorted() function sorts numbers numerically:

my_list = [123, 99, 23, 25, 1]
x = sorted(my_list)
print(x) # Output: [1, 23, 25, 99, 123]

output

[1, 23, 25, 99, 123]
note

If you want to sort the list in-place, use built-in sort() method of lists.

Example 3: Sort a Tuple​

numbers = (4, 25, 23, 6, 8, 15)
print(sorted(numbers)) # Output: [1, 2, 4, 6, 8, 15]

output

[4, 6, 8, 15, 23, 25]

Example 4: Sort a Dictionary by Keys​

sorted() function sorts a dictionary by keys, by default.

my_dict = {1: 'one', 2: 'two', 3: 'three'}
print(sorted(my_dict)) # Output: [1, 2, 3]

output

[1, 2, 3]

Example 5: Sort a Dictionary by Values​

To sort a dictionary by values use the sorted() function along with the values() method.

my_dict = {1: 'one', 2: 'two', 3: 'three'}
x = sorted(my_dict.values())
print(x) # Output: ['one', 'three', 'two']

output

['one', 'three', 'two']

Example 6: Sort in reverse order​

You can also sort an iterable in reverse order by setting reverse parameter to True.

numbers = [4, 25, 23, 6, 8, 15]
x = sorted(numbers, reverse=True)
print(x) # Output: [25, 23, 15, 8, 6, 4]

output

[25, 23, 15, 8, 6, 4]

Example 7: Sort with Key parameter​

You can use key parameter for more complex custom sorting. A key parameter specifies a function to be executed on each list item before making comparisons.

For example, with a list of strings, specifying key=len (the built-in len() function) sorts the strings by length, from shortest to longest.

my_list = ['orange', 'red', 'green', 'blue']
x = sorted(my_list, key=len)
print(x) # Output: ['red', 'blue', 'green', 'orange']

output

['red', 'blue', 'green', 'orange']

Example 8: Sort using Custom Function​

You can also pass to the sorted() function your own custom function as key function. A key function should take a single argument and return a key to use for sorting.

For example, sort a list of students (as list of tuple) by age (second element of the tuple):

def sortByAge(e):
  return e[1]	# return age

students = [('Tom', 30),('Anna', 23), ('Dave', 25)]
x = sorted(students, key=sortByAge)
print(x) # Output: [('Anna', 23), ('Dave', 25), ('Tom', 30)]

output

[('Anna', 23), ('Dave', 25), ('Tom', 30)]

Example 9: Sort using Lambda​

A key function may also be created with the lambda expression. It allows us to in-line function definition.

For example, sort a list of students (as list of tuple) by age (second element of the tuple):

students = [('Tom', 30),('Anna', 23), ('Dave', 25)]
x = sorted(students, key=lambda student: student[1])
print(x) # Output: [('Anna', 23), ('Dave', 25), ('Tom', 30)]

output

[('Anna', 23), ('Dave', 25), ('Tom', 30)]

Example 10: Sort using Operator Module Functions​

To access items of an iterable, Python provides convenience functions like itemgetter() and attrgetter() from operator module.

For example, sort a list of students (as list of tuple) by age (second element of the tuple):

from operator import itemgetter

students = [('Tom', 30),('Anna', 23), ('Dave', 25)]
x = sorted(students, key=itemgetter(1))
print(x) # Output: [('Anna', 23), ('Dave', 25), ('Tom', 30)]

output

[('Anna', 23), ('Dave', 25), ('Tom', 30)]

Example 11: Multiple Level Sorting (nested sorting)​

The operator module functions allow multiple levels of sorting as well.

For example, sort students by grade and then by age:

from operator import itemgetter

students = [('Bob', 'B', 30),
	        ('Anna', 'A', 23),
            ('Max', 'B', 18),
            ('Tom', 'A', 29),
            ('Dave', 'A', 25),
            ('Ryan', 'B', 15)]
x = sorted(students, key=itemgetter(1,2))
print(x) # [('Anna', 'A', 23), ('Dave', 'A', 25), ('Tom', 'A', 29), ('Ryan', 'B', 15), ('Max', 'B', 18), ('Bob', 'B', 30)]

output

[('Anna', 'A', 23), ('Dave', 'A', 25), ('Tom', 'A', 29), ('Ryan', 'B', 15), ('Max', 'B', 18), ('Bob', 'B', 30)]

Example 12: Sort Custom Objects​

Consider a list of custom objects:

class Student:
	def __init__(self, name, grade, age):
		self.name = name
		self.grade = grade
		self.age = age
	def __repr__(self):
		return repr((self.name, self.grade, self.age))

# a list of custom objects
my_list = [Student('Bob', 'B', 30),
	        Student('Dave', 'A', 25),
	        Student('Anna', 'B', 23)]

Then, there are different techniques to sort my_list list of custom objects:

# with lambda
result_lambda = sorted(my_list, key=lambda student: student.age)
print(result_lambda) # [('Anna', 'B', 23), ('Dave', 'A', 25), ('Bob', 'B', 30)]

output

[('Anna', 'B', 23), ('Dave', 'A', 25), ('Bob', 'B', 30)]
# with attrgetter
from operator import attrgetter

result_attrgetter = sorted(my_list, key=attrgetter('age'))
print(result_attrgetter) # [('Anna', 'B', 23), ('Dave', 'A', 25), ('Bob', 'B', 30)]

output

[('Anna', 'B', 23), ('Dave', 'A', 25), ('Bob', 'B', 30)]
# Multiple Level Sorting with custom objects
from operator import attrgetter

# Sort by grade and then by age
result_multi_level = sorted(my_list, key=attrgetter('grade', 'age'))
print(result_multi_level) # [('Dave', 'A', 25), ('Anna', 'B', 23), ('Bob', 'B', 30)]

output

[('Dave', 'A', 25), ('Anna', 'B', 23), ('Bob', 'B', 30)]

Example 13: Sort a List of Tuples by a Specific Element​

For example, let's sort a list of tuples based on the first element of each tuple.

A lambda function is passed as the key argument to sorted() function, specifying that the sorting should be done based on the first element of each tuple.

my_tuples = [(4, 'banana'), (1, 'apple'), (3, 'cherry'), (2, 'orange')]
sorted_tuples = sorted(my_tuples, key=lambda x: x[0])
print(sorted_tuples)  # Output: [(1, 'apple'), (2, 'orange'), (3, 'cherry'), (4, 'banana')]

output

[(1, 'apple'), (2, 'orange'), (3, 'cherry'), (4, 'banana')]

Example 14: Sort a List of Dictionaries by a Specific Key​

For example, let's sort a list of dictionaries based on the value of a specific key. In this case we sort based on the age key of each dictionary.

my_dicts = [{'name': 'Tom', 'age':  26}, {'name': 'Dave', 'age':  25}, {'name': 'Anna', 'age':  23}]
sorted_dicts = sorted(my_dicts, key=lambda x: x['age'])
print(sorted_dicts)  # Output: [{'name': 'Anna', 'age': 23}, {'name': 'Dave', 'age': 25}, {'name': 'Tom', 'age': 26}]

output

[{'name': 'Anna', 'age': 23}, {'name': 'Dave', 'age': 25}, {'name': 'Tom', 'age': 26}]

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