Dictionary in Python

Lecture 16:- Dictionary in Python

In Python, a dictionary is a versatile and powerful data structure that allows you to store a collection of key-value pairs. Dictionaries are also known as associative arrays or hash maps in other programming languages. Dictionaries are defined by enclosing a comma-separated list of key-value pairs within curly braces { }.

Here's a brief introduction to dictionaries in Python:

1. Creating a Dictionary: You can create a dictionary by defining it with curly braces and specifying key-value pairs separated by colons.

Example:

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# Dictionary of key-value pairs with strings as keys person = {    "name": "John",    "age": 30,    "city": "New York" } # Dictionary of key-value pairs with integers as keys grades = {    101: "A",    102: "B",    103: "C" } # Mixed data types as values in a dictionary data = {    "name": "Alice",    "age": 25,    "is_student": True,    "marks": [90, 95, 85] }

1. Accessing Values: You can access the values in a dictionary by using the corresponding key.

Example:

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person = {    "name": "John",    "age": 30,    "city": "New York" } print(person["name"])   # Output: John print(person["age"])    # Output: 30

1. Modifying and Adding Elements: Dictionaries are mutable, so you can change the value associated with a key or add new key-value pairs.

Example:

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person = {    "name": "John",    "age": 30,    "city": "New York" } person["age"] = 35    # Modify the value for the key "age" print(person)         # Output: {'name': 'John', 'age': 35, 'city': 'New York'} person["occupation"] = "Engineer"   # Add a new key-value pair print(person)                       # Output: {'name': 'John', 'age': 35, 'city': 'New York', 'occupation': 'Engineer'}

1. Dictionary Methods: Dictionaries come with various built-in methods to perform common operations, such as keys(), values(), items(), get(), pop(), update(), etc. These methods provide convenient ways to manipulate dictionaries.

Example:

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person = {    "name": "John",    "age": 30,    "city": "New York" } print(person.keys())      # Output: dict_keys(['name', 'age', 'city']) print(person.values())    # Output: dict_values(['John', 30, 'New York']) print(person.items())     # Output: dict_items([('name', 'John'), ('age', 30), ('city', 'New York')]) print(person.get("name"))     # Output: John print(person.get("gender"))   # Output: None

Dictionaries are widely used for various purposes, such as representing data in key-value pairs, mapping values to unique identifiers, and organizing data for efficient access and retrieval. They are an essential part of Python and are commonly used in many real-world applications.