Python sorted() & key Functions
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Standard Sorting with sorted()
sorted(iterable) returns a brand-new sorted list, leaving the original iterable untouched -- distinct from a list's own .sort() method, which sorts in place and returns None. Reaching for the wrong one is a common source of confusing bugs where a variable unexpectedly becomes None.
Example: Standard Sorting with sorted()
numbers = [3, 1, 2]
result = sorted(numbers)
print(result, numbers)Sorting in Reverse Order
sorted() orders elements ascending by default; passing reverse=True flips that to descending order without needing to sort ascending and then separately reverse the result.
Example: Sorting in Reverse Order
numbers = [3, 1, 2]
print(sorted(numbers, reverse=True))Sorting with Custom Key Functions
The key parameter accepts a function that's applied to each element to compute the value actually used for comparison, letting you sort by a derived property (like a string's length) rather than the elements' natural ordering.
Example: Sorting with Custom Key Functions
words = ["banana", "kiwi", "apple"]
print(sorted(words, key=len))Sorting with Lambda Keys
A lambda is the typical way to supply a key function inline, especially for simple derivations like key=lambda x: x[1] to sort tuples by their second element, without the overhead of defining a separate named function elsewhere.
Example: Sorting with Lambda Keys
pairs = [(1, "b"), (2, "a")]
print(sorted(pairs, key=lambda x: x[1]))Sorting Complex Lists
Sorting a list of dictionaries or custom objects by a specific field is the most common real-world use of key -- sorted(people, key=lambda p: p[age]), for instance, sorts a list of person-records by age without needing any custom comparison logic beyond naming which field matters.
Example: Sorting Complex Lists
people = [{"name": "Alex", "age": 30}, {"name": "Sam", "age": 25}]
print(sorted(people, key=lambda p: p["age"]))Chapter Quiz — Complete all 15 topics to unlock
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- Python sorted() & key Functions
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