python itemgetter with examples.

itemgetter.md

The itemgetter function from Python's operator module creates a callable that retrieves items from objects using indices (for sequences like lists/tuples) or keys (for mappings like dictionaries). It is efficient and commonly used with functions like sorted(), max(), and min() for clean, readable code.

Importing itemgetter

from operator import itemgetter

Examples

1. Basic Usage with a List

   data = ['a', 'b', 'c', 'd']
   
   get_second = itemgetter(1)
   print(get_second(data))  # Output: 'b'
   
   get_multiple = itemgetter(1, 3)
   print(get_multiple(data))  # Output: ('b', 'd')

2. Using with Dictionaries

   person = {'name': 'Alice', 'age': 30, 'job': 'Engineer'}
   
   get_age = itemgetter('age')
   print(get_age(person))  # Output: 30

3. Sorting a List of Tuples

   students = [('Alice', 85, 20), ('Bob', 75, 22), ('Charlie', 90, 21)]
   
   # Sort by grade (index 1)
   sorted_by_grade = sorted(students, key=itemgetter(1))
   print(sorted_by_grade)  # Output: [('Bob', 75, 22), ('Alice', 85, 20), ('Charlie', 90, 21)]

4. Sorting a List of Dictionaries by Multiple Keys

   people = [
       {'name': 'Alice', 'age': 30},
       {'name': 'Bob', 'age': 25},
       {'name': 'Charlie', 'age': 30}
   ]
   
   # Sort by 'age', then 'name'
   sorted_people = sorted(people, key=itemgetter('age', 'name'))
   print(sorted_people)
   # Output: [{'name': 'Bob', 'age': 25}, {'name': 'Alice', 'age': 30}, {'name': 'Charlie', 'age': 30}]

5. Finding Maximum Using itemgetter

   max_student = max(students, key=itemgetter(1))
   print(max_student)  # Output: ('Charlie', 90, 21)

Comparison with lambda

• itemgetter(1) is equivalent to lambda x: x[1].
• Advantages of itemgetter:
  • Readability: Clearly expresses intent.
  • Performance: Faster for large datasets due to C-level optimization.

Key Takeaways

• Use itemgetter to cleanly extract items by index/key.
• Ideal for sorting, finding max/min, or extracting data from nested structures.
• Supports multiple indices/keys to return tuples for multi-level comparisons.