Custom Sorting in Python

This article introduces various methods to customize sorting in Python, including using sorted() function, list's .sort() method, and custom comparison functions.

1. Using sorted() function: The sorted() function can sort any iterable and return a new sorted list. You can customize the sorting logic using the key parameter.

1.1 Example: Sorting by string length

def sort_by_length(strings): return sorted(strings, key=len) strings = ["hello", "world", "python", "code"] sorted_strings = sort_by_length(strings) print(sorted_strings) # Output: ["code", "hello", "world", "python"]

1.2 Example: Descending order

def sort_by_length_desc(strings): return sorted(strings, key=len, reverse=True) strings = ["hello", "world", "python", "code"] sorted_strings = sort_by_length_desc(strings) print(sorted_strings) # Output: ["python", "world", "hello", "code"]

2. Using list's .sort() method: This method sorts the list in-place. Use the key parameter for custom sorting.

2.1 Example: Sorting by string length

def sort_by_length_inplace(strings): strings.sort(key=len) strings = ["hello", "world", "python", "code"] sort_by_length_inplace(strings) print(strings) # Output: ["code", "hello", "world", "python"]

2.2 Example: Descending order

def sort_by_length_desc_inplace(strings): strings.sort(key=len, reverse=True) strings = ["hello", "world", "python", "code"] sort_by_length_desc_inplace(strings) print(strings) # Output: ["python", "world", "hello", "code"]

3. Using custom comparison functions: Although Python 3 doesn't support cmp, you can use functools.cmp_to_key.

3.1 Example: Ascending order

from functools import cmp_to_key def compare_strings(s1, s2): if len(s1) < len(s2): return -1 elif len(s1) > len(s2): return 1 else: return 0 def sort_by_length_cmp(strings): return sorted(strings, key=cmp_to_key(compare_strings)) strings = ["hello", "world", "python", "code"] sorted_strings = sort_by_length_cmp(strings) print(sorted_strings) # Output: ["code", "hello", "world", "python"]

3.2 Example: Descending order

from functools import cmp_to_key def compare_strings(s1, s2): if len(s1) < len(s2): return 1 elif len(s1) > len(s2): return -1 else: return 0 def sort_by_length_desc_cmp(strings): return sorted(strings, key=cmp_to_key(compare_strings)) strings = ["hello", "world", "python", "code"] sorted_strings = sort_by_length_desc_cmp(strings) print(sorted_strings) # Output: ["python", "world", "hello", "code"]

4. Example: Combining sorting logic

def sort_strings(strings): return sorted(strings, key=lambda s: (len(s), s)) strings = ["hello", "world", "python", "code", "coding"] sorted_strings = sort_strings(strings) print(sorted_strings) # Output: ["code", "coding", "hello", "world", "python"]

5. Using operator.itemgetter: Sort by object attributes.

import operator class Person: def __init__(self, name, age): self.name = name self.age = age def __repr__(self): return f"Person({self.name}, {self.age})" people = [ Person("Alice", 25), Person("Bob", 30), Person("Charlie", 20), Person("David", 35) ] def sort_people_by_age(people): return sorted(people, key=operator.attrgetter("age")) sorted_people = sort_people_by_age(people) print(sorted_people) # Output: [Person(Charlie, 20), Person(Alice, 25), Person(Bob, 30), Person(David, 35)]

6. Using functools.partial: Sort based on a custom key function.

import functools def custom_sort_key(person): return person.age + len(person.name) class Person: def __init__(self, name, age): self.name = name self.age = age def __repr__(self): return f"Person({self.name}, {self.age})" people = [ Person("Alice", 25), Person("Bob", 30), Person("Charlie", 20), Person("David", 35) ] def sort_people_custom_key(people): custom_key = functools.partial(custom_sort_key) return sorted(people, key=custom_key) sorted_people = sort_people_custom_key(people) print(sorted_people) # Output: [Person(Charlie, 20), Person(Alice, 25), Person(Bob, 30), Person(David, 35)]

7. Conclusion: This article covers various methods to customize sorting in Python, including using sorted() function, list's .sort() method, custom comparison functions, combining sorting logic, using operator.itemgetter, and functools.partial.