How to Sort a List of Dictionaries by Key with a Lambda in Python

Sort a list of dictionaries ascending or descending by one of their keys using sorted() with a lambda as the key function — a beginner-friendly pattern.

Easy Python 3.8+ Aug 9, 2026 Functions & basics 13 views 0 copies

sorting lambda dictionaries sorted

Python code

19 lines

Python 3.8+

def get_students():
    return [
        {"name": "alice", "score": 85},
        {"name": "bob", "score": 92},
        {"name": "carol", "score": 78},
        {"name": "dave", "score": 92},
    ]

students = get_students()

sorted_by_score = sorted(students, key=lambda s: s["score"])
print("Sorted by score (ascending):")
for student in sorted_by_score:
    print(f"  {student['name']} - {student['score']}")

sorted_by_score_desc = sorted(students, key=lambda s: s["score"], reverse=True)
print("\nSorted by score (descending):")
for student in sorted_by_score_desc:
    print(f"  {student['name']} - {student['score']}")

Output

stdout

Sorted by score (ascending):
  carol - 78
  alice - 85
  bob - 92
  dave - 92

Sorted by score (descending):
  bob - 92
  dave - 92
  alice - 85
  carol - 78

How it works

The sorted() function takes an iterable and returns a new sorted list. The key parameter receives a function that is called on each element to extract the value to sort by. A lambda lambda s: s["score"] is a concise way to pull out the score key from each dictionary. Setting reverse=True reverses the order, giving descending output. Because sorted is stable, students with equal scores keep their original relative order (bob before dave in the descending example).

Common mistakes

Forgetting to specify the key, which would sort by the dictionary's hash, raising an error.
Using `students.sort()` instead of `sorted()` to avoid modifying the original list.
Confusing ascending vs descending — remember `reverse=True` for descending.

Variations

Sort by multiple keys: `sorted(students, key=lambda s: (s["score"], s["name"]))`.
Sort in place with `students.sort(key=lambda s: s["score"])`.

Real-world use cases

Sorting a list of user records from a database by registration date before displaying a leaderboard.
Ordering log entries by timestamp when processing a batch of events.
Ranking products by price or rating in an e-commerce API response.

How to Sort a List of Dictionaries by Key with a Lambda in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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