Dictionaries in Python

What is a Dictionary?

A dictionary in Python is an unordered collection of data in a key-value pair format. Dictionaries are mutable and indexed by keys, which can be any immutable type.

Syntax:

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

Creating a Dictionary

You can create a dictionary in several ways:

# Using curly braces
student = {"name": "John", "grade": "A"}

# Using the dict() constructor
student = dict(name="John", grade="A")

Accessing Elements

Use the key inside square brackets or the get() method.

name = student["name"]
grade = student.get("grade")

Modifying Elements

You can update a value using the assignment operator.

student["grade"] = "A+"

Adding Elements

To add a new key-value pair:

student["age"] = 20

Removing Elements

Several methods can be used:

del student["age"]
student.pop("grade")
student.clear()  # Removes all items

Dictionary Methods

Common methods used with dictionaries:

keys = student.keys()
values = student.values()
items = student.items()

Iterating Through a Dictionary

for key, value in student.items():
    print(key, value)

Nested Dictionaries

people = {
    "person1": {"name": "Alice", "age": 25},
    "person2": {"name": "Bob", "age": 30}
}

Dictionary Comprehension

squares = {x: x*x for x in range(5)}

Real-Life Usage Examples

Machine Learning: Feature Representation

Dictionaries are used for encoding features before passing to models.

sample = {
    "age": 29,
    "gender": "female",
    "income": 45000
}

features = {
    "age": sample["age"],
    "gender_female": 1 if sample["gender"] == "female" else 0,
    "income": sample["income"]
}

Chatbot Intent Mapping

Mapping user intents to bot responses using dictionaries.

intents = {
    "greeting": "Hello! How can I help you today?",
    "farewell": "Goodbye! Have a great day.",
    "thanks": "You're welcome!"
}

user_input = "greeting"
print(intents.get(user_input, "Sorry, I didn’t understand that."))

Configuration Settings

Storing application settings in dictionaries for easy access and modification.

config = {
    "debug": True,
    "database_uri": "sqlite:///mydb.db",
    "max_connections": 20
}

if config["debug"]:
    print("Debug mode is ON")