Dictionaries

Understanding Dictionaries

A dictionary in Python is an unordered collection of key-value pairs. It's similar to a real-world dictionary where you look up a word (key) to find its meaning (value). Dictionaries are defined by enclosing key-value pairs within curly braces {}.

Creating a Dictionary

Python

my_dict = {'name': 'Alice', 'age': 30, 'city': 'New York'}

In this example, 'name', 'age', and 'city' are keys, and their corresponding values are 'Alice', 30, and 'New York'.

Accessing Dictionary Elements

You can access values using their corresponding keys:

Python

my_dict = {'name': 'Alice', 'age': 30}

name = my_dict['name']  # Accessing the value associated with the key 'name'

print(name)  # Output: Alice

Modifying Dictionaries

Dictionaries are mutable, so you can change, add, or remove key-value pairs:

Python

my_dict = {'name': 'Alice', 'age': 30}

my_dict['age'] = 31  # Modifying the value of an existing key

my_dict['city'] = 'Los Angeles'  # Adding a new key-value pair

del my_dict['age']  # Removing a key-value pair

Dictionary Methods

Python provides several methods for working with dictionaries:

• keys(): Returns a view of the dictionary's keys.

• values(): Returns a view of the dictionary's values.

• items(): Returns a view of the dictionary's key-value pairs as tuples.

• get(key, default): Returns the value for the specified key. If the key is not found, returns the default value (None if not specified).

• pop(key, default): Removes and returns the value for the specified key. If the key is not found, returns the default value (raises a KeyError if not specified).

• update(other_dict): Updates the dictionary with the key-value pairs from another dictionary.

Example

Python

my_dict = {'name': 'Alice', 'age': 30}

keys = my_dict.keys()

values = my_dict.values()

items = my_dict.items()

print(keys)  # Output: dict_keys(['name', 'age'])

print(values)  # Output: dict_values(['Alice', 30])

print(items)  # Output: dict_items([('name', 'Alice'), ('age', 30)])

Important Points

• Dictionary keys must be immutable (e.g., strings, numbers, tuples).

• Dictionaries are unordered, meaning the order of elements is not guaranteed.

• Dictionaries are efficient for lookups based on keys.

Dictionaries are a powerful data structure in Python, widely used for representing data with key-value relationships