Dictionaries in Python

Dictionaries are one of the most powerful and widely used data structures in Python. A dictionary is an unordered, mutable collection of items stored as key-value pairs.

Creating Dictionaries

Dictionaries are created using curly braces {} with keys and values separated by colons :.

# A simple dictionary
person = {
    "name": "Alice",
    "age": 25,
    "city": "New York"
}

# Empty dictionary
empty_dict = {}

# Dictionary with mixed value types
data = {
    "colors": ["red", "blue"],
    "is_active": True,
    "count": 10
}

Accessing and Modifying Values

You can access a value by referring to its key name, inside square brackets.

person = {"name": "Alice", "age": 25}

# Accessing
print(person["name"])  # Output: Alice

# Modifying
person["age"] = 26

# Adding a new key-value pair
person["email"] = "alice@example.com"

Common Dictionary Methods

Python provides several built-in methods for working with dictionaries.

Method	Description
get(key)	Returns the value of the specified key; returns None if key doesn’t exist
keys()	Returns a list of all keys in the dictionary
values()	Returns a list of all values in the dictionary
items()	Returns a list of tuples for each key-value pair
update({key: value})	Updates the dictionary with the specified key-value pairs
pop(key)	Removes the element with the specified key
clear()	Removes all elements from the dictionary

car = {"brand": "Ford", "model": "Mustang", "year": 1964}

print(car.get("brand")) # Output: Ford
print(car.keys())       # Output: dict_keys(['brand', 'model', 'year'])

Looping Through a Dictionary

You can loop through a dictionary using a for loop.

person = {"name": "Alice", "age": 25}

# Loop through keys
for key in person:
    print(key)

# Loop through values
for val in person.values():
    print(val)

# Loop through both (items)
for key, value in person.items():
    print(f"{key}: {value}")

Nested Dictionaries

A dictionary can also contain other dictionaries.

users = {
    "user1": {"name": "Alice", "age": 25},
    "user2": {"name": "Bob", "age": 30}
}

print(users["user1"]["name"]) # Output: Alice