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Python Dictionaries (with Examples)

Jason Smith
By Jason Smith
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Python Dictionaries (with Examples)

A dictionary in Python is a collection of key-value pairs. It is one of Python’s built-in data structures and is used to store data values like a map. Each key in a dictionary must be unique, immutable, and is associated with a value.

Characteristics of a Dictionary

  1. Unordered: The items are stored in an unordered manner (as of Python 3.7, dictionaries maintain insertion order).
  2. Mutable: You can add, modify, or remove items.
  3. Keys are Unique: No duplicate keys are allowed.
  4. Keys Must Be Immutable: Keys can be strings, numbers, or tuples (not lists or other dictionaries).

Creating a Dictionary

1. Using Curly Braces

python
my_dict = {
"name": "Alice",
"age": 25,
"city": "New York"
}
print(my_dict)
# Output: {'name': 'Alice', 'age': 25, 'city': 'New York'}

2. Using the dict() Constructor

python
my_dict = dict(name="Bob", age=30, city="Los Angeles")
print(my_dict)
# Output: {'name': 'Bob', 'age': 30, 'city': 'Los Angeles'}

Accessing Dictionary Items

  1. Using Keys
python
my_dict = {"name": "Alice", "age": 25}
print(my_dict["name"]) # Output: Alice
  1. Using the get() Method
python
print(my_dict.get("age")) # Output: 25
print(my_dict.get("gender", "Not Specified")) # Output: Not Specified

Adding and Modifying Items

python
my_dict = {"name": "Alice", "age": 25}
my_dict["city"] = "New York" # Add new key-value pair
my_dict["age"] = 26 # Modify existing key
print(my_dict)
# Output: {'name': 'Alice', 'age': 26, 'city': 'New York'}

Removing Items

  1. Using pop()
python
my_dict = {"name": "Alice", "age": 25, "city": "New York"}
my_dict.pop("age")
print(my_dict)
# Output: {'name': 'Alice', 'city': 'New York'}
  1. Using del
python
del my_dict["city"]
print(my_dict)
# Output: {'name': 'Alice'}
  1. Using clear()
python
my_dict.clear()
print(my_dict)
# Output: {}

Iterating Through a Dictionary

  1. Keys Only
python
my_dict = {"name": "Alice", "age": 25}
for key in my_dict:
print(key)
# Output: name
# age
  1. Values Only
python
for value in my_dict.values():
print(value)
# Output: Alice
# 25
  1. Keys and Values
python
for key, value in my_dict.items():
print(f"{key}: {value}")
# Output: name: Alice
# age: 25

Checking for Keys

python
my_dict = {"name": "Alice", "age": 25}
print("name" in my_dict) # Output: True
print("gender" in my_dict) # Output: False

Dictionary Methods

Method Description
get(key, default) Returns the value for the specified key.
keys() Returns a view object of all the keys.
values() Returns a view object of all the values.
items() Returns a view object of all the key-value pairs.
pop(key) Removes the specified key and returns its value.
popitem() Removes and returns the last inserted key-value pair (from Python 3.7 onward).
clear() Removes all items from the dictionary.
update(other_dict) Updates the dictionary with items from another dictionary or iterable.
See also  What Is Computer Science?

Examples of Real-World Usage

  1. Storing User Data
python
user = {"username": "johndoe", "email": "[email protected]", "is_active": True}
  1. Counting Occurrences
python
from collections import Counter

text = "apple banana apple orange"
word_count = Counter(text.split())
print(word_count)
# Output: {'apple': 2, 'banana': 1, 'orange': 1}

  1. Representing JSON Data
python
import json

data = '{"name": "Alice", "age": 25, "city": "New York"}'
parsed = json.loads(data)
print(parsed)
# Output: {'name': 'Alice', 'age': 25, 'city': 'New York'}

Dictionaries are a versatile and essential tool in Python, enabling efficient storage and manipulation of data through key-value pairs.

Related posts:

  1. When was the First Computer Invented?
  2. How to Convert Uppercase to Lowercase in Microsoft Word
  3. What Is Computer Science?
  4. What Can Computer Science Do?
  5. What Is Computer Science Major?
  6. What Is Computer Science Engineering?
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