Dictionaries are Python’s built-in mapping type for storing key-value pairs.

Method 1: Curly Brace Notation

The most common way to create a dictionary:

# Empty dictionary
empty_dict = {}

# Dictionary with items
person = {
    "name": "Alice",
    "age": 25,
    "city": "Paris"
}

print(person["name"])  # Alice

Method 2: dict() Constructor

Create dictionaries using the constructor:

# From keyword arguments
person = dict(name="Alice", age=25, city="Paris")

# From list of tuples
items = [("name", "Bob"), ("age", 30)]
person = dict(items)

print(person)  # {'name': 'Bob', 'age': 30}

Method 3: Dictionary Comprehension

Create dictionaries with a concise syntax:

# Squares of numbers
squares = {x: x**2 for x in range(5)}
print(squares)  # {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

# From two lists
keys = ["a", "b", "c"]
values = [1, 2, 3]
my_dict = {k: v for k, v in zip(keys, values)}
print(my_dict)  # {'a': 1, 'b': 2, 'c': 3}

Method 4: fromkeys()

Create a dictionary with default values:

keys = ["name", "age", "city"]
default_dict = dict.fromkeys(keys, "unknown")
print(default_dict)  # {'name': 'unknown', 'age': 'unknown', 'city': 'unknown'}

Accessing and Modifying Values

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

# Access value
print(person["name"])      # Alice
print(person.get("city"))  # None (safe access)
print(person.get("city", "N/A"))  # N/A (with default)

# Add or update
person["city"] = "Paris"
person["age"] = 26

# Remove
del person["age"]
city = person.pop("city")  # Removes and returns value

Useful Methods

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

# Get all keys
print(person.keys())    # dict_keys(['name', 'age'])

# Get all values
print(person.values())  # dict_values(['Alice', 25])

# Get key-value pairs
print(person.items())   # dict_items([('name', 'Alice'), ('age', 25)])

# Check if key exists
print("name" in person)  # True

Summary

Use {} for quick dictionary creation
Use dict() for creating from other structures
Use dictionary comprehensions for transformations
Use .get() for safe access with default values

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