Dictionaries in Python: 4 Essential Techniques to Master

Dictionaries in Python are incredibly versatile and essential for many programming tasks. They allow you to store data as key-value pairs, making them perfect for organizing and accessing information efficiently.

In this guide, we’ll dive into creating, updating, and using dictionaries, exploring advanced techniques like nested dictionaries and the helpful defaultdict.

1. Creating and Accessing Dictionaries: Key-Value Pairs

Dictionaries are defined using curly braces {}. Each item consists of a key and its associated value, separated by a colon (:).

animals = {'a': 'aardvark', 'b': 'bear', 'c': 'caribou'}

To access a value, use its corresponding key:

print(animals['a'])  # Output: aardvark

Trailing Commas: It’s good practice to use trailing commas in dictionaries for better readability and easier future modifications.

2. Modifying Dictionaries: Add, Update, Get

• Adding a New Key-Value Pair:

animals['d'] = 'dog'

• Updating an Existing Value:

animals['a'] = 'antelope'

• Retrieving Keys and Values:

keys = list(animals.keys())    # Convert to list for manipulation
values = list(animals.values())

• Safely Getting Values:

animal = animals.get('e', 'elephant') # Returns 'elephant' if 'e' doesn't exist

3. Nested Dictionaries: Organizing Complex Data

Dictionaries can hold other dictionaries as values, creating nested structures:

animals = {'a': ['aardvark', 'antelope'], 'b': ['bear', 'bison']}

To access nested values, chain keys together:

print(animals['b'][1])  # Output: bison

4. Defaultdict: Simplifying Appends and Creation

The defaultdict from the collections module streamlines working with dictionaries that hold lists as values. If a key doesn’t exist, it automatically creates an empty list for you.

from collections import defaultdict

animals = defaultdict(list)  # Creates a defaultdict with empty lists as default values

animals['c'].append('cat')
animals['e'].append('elephant')
animals['e'].append('emu')

print(animals['f'])  # Output: [] (empty list, no KeyError)

Frequently Asked Questions (FAQ)

del animals['a']

for key, value in animals.items():
    print(key, value)