How to Sort a List of Dictionaries by Key in Python

Sort a list of dictionaries by various keys (grade, age, name) using lambda, itemgetter, and extract unique sorted names into a set.

Easy Python 3.9+ Aug 9, 2026 Dictionaries & sets 12 views 0 copies

sorting dictionaries sets itemgetter lambda

Python code

32 lines

Python 3.9+

from operator import itemgetter

# Sample data: a list of dictionaries representing students
students = [
    {"name": "Alice", "grade": 88, "age": 23},
    {"name": "Bob", "grade": 95, "age": 22},
    {"name": "Charlie", "grade": 78, "age": 24},
    {"name": "Diana", "grade": 92, "age": 21}
]

# Sort by grade (descending) using lambda
by_grade_desc = sorted(students, key=lambda s: s["grade"], reverse=True)

# Sort by age (ascending) using itemgetter
by_age_asc = sorted(students, key=itemgetter("age"))

# Sort by name (alphabetic) and extract just names into a set
names_sorted = sorted(s["name"] for s in students)
unique_names = set(names_sorted)

if __name__ == "__main__":
    print("Sorted by grade (high to low):")
    for s in by_grade_desc:
        print(f"  {s['name']}: {s['grade']}")

    print("\nSorted by age (low to high):")
    for s in by_age_asc:
        print(f"  {s['name']}: {s['age']}")

    print("\nUnique names, sorted:")
    for name in unique_names:
        print(f"  {name}")

Output

stdout

Sorted by grade (high to low):
  Bob: 95
  Diana: 92
  Alice: 88
  Charlie: 78

Sorted by age (low to high):
  Diana: 21
  Bob: 22
  Alice: 23
  Charlie: 24

Unique names, sorted:
  Alice
  Bob
  Charlie
  Diana

How it works

The sorted() function returns a new list, leaving the original students list untouched. Using key=lambda s: s["grade"] extracts a specific value from each dictionary for comparison. itemgetter("age") from the operator module is a faster, more readable alternative for simple key lookups. The generator expression s["name"] for s in students collects names, which sorted() orders alphabetically, and set() removes duplicates while preserving uniqueness.

Common mistakes

Forgetting `reverse=True` when you want descending order — default is ascending.
Using `.sort()` on the original list when you need to keep the original data unchanged.
Assuming keys exist without checking — a missing key raises `KeyError` during sorting.

Variations

Use `key=lambda s: (-s["grade"], s["name"])` for multi-level sorting (grade desc, then name asc).
For data with many dictionary keys, `itemgetter("age", "grade")` can sort by multiple fields at once.

Real-world use cases

Ranking user profiles by score in a leaderboard API before returning results.
Sorting product records by price or popularity in an e-commerce catalog.
Deduplicating and alphabetizing a list of employee names pulled from a database.

How to Sort a List of Dictionaries by Key in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Dictionaries & sets

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