Python Dictionaries: A Simple Guide
In Python, a dictionary is a data structure that stores data in pairs of keys and values. Unlike lists, where items are accessed by their position (index), dictionaries allow you to access data by using a unique key, making it very efficient for looking up information.
Basics of Python Dictionaries
A dictionary is defined using curly braces {} with key-value pairs inside, where each key is followed by its value and separated by a colon (:).
Here’s an example:
In this example:
The keys are
"name"and"age".The values are
"John"and25.
You can think of the key as a label and the value as the actual data.
How to Access Data in a Dictionary
To access a value in a dictionary, you use the key in square brackets []:
Common Use Cases for Dictionaries
1. Storing User Details
Dictionaries are ideal for storing related information about an entity, such as user details, where you can quickly look up the information using a descriptive key
2. Counting Occurrences
You can use dictionaries to count how many times something appears. For example, counting the number of times each word appears in a list:
Tips for Using Dictionaries Effectively
Keys Must Be Unique and Immutable:
Dictionary keys must be unique; you can’t have two identical keys. If you assign a new value to an existing key, the old value gets replaced.
Keys must be immutable, which means they can’t change. This is why you can use strings or numbers as keys, but not lists (since lists are mutable).
Using .get() to Avoid Key Errors:
When accessing a key that may or may not exist, use the .get() method. This ensures that your program won’t crash if the key is missing.
Summary
Python dictionaries are powerful data structures that store data in key-value pairs, making them ideal for fast lookups, counting occurrences, and storing related information. The keys must be unique and immutable, while the values can be anything. By using methods like .get(), you can safely access data without running into errors if the key doesn’t exist. With these tips, you can use dictionaries effectively in your Python projects.
References & Further Reading
https://docs.python.org/3/tutorial/datastructures.html#dictionaries