Python - Dictionaries

In Python, a dictionary is a collection of key-value pairs. Each key must be unique within a dictionary, and it maps to a specific value. Dictionaries are defined using curly braces {}.

# Example dictionary
person = {
    "Name": "John",
    "Age": 25,
    "City": "New York"
}

# Accessing values using keys
print("Name:", person["Name"])
print("Age:", person["Age"])
print("City:", person["City"])

Output:

Name: John
Age: 25
City: New York

In Python, you can create an empty dictionary using curly braces {} or by using the built-in dict() constructor.

# Using curly braces
empty_dict1 = {}
print("Empty Dictionary 1:", empty_dict1)

# Using dict() constructor
empty_dict2 = dict()
print("Empty Dictionary 2:", empty_dict2)

Output:

Empty Dictionary 1: {}
Empty Dictionary 2: {}

In Python, dictionaries are a collection of key-value pairs. Here are key characteristics of dictionaries:

1. Unordered: Dictionaries are unordered, meaning that the order of elements is not guaranteed.
2. Mutable: You can modify dictionaries by adding, updating, or removing key-value pairs.
3. Dynamic: Dictionaries can grow or shrink in size as needed.
4. Keys: Keys in a dictionary must be unique and immutable (strings, numbers, or tuples).
5. Values: Values in a dictionary can be of any data type and can be duplicated.

Here's an example demonstrating the key characteristics:

# Creating a dictionary
student_info = {
    "Name": "John",
    "Age": 25,
    "City": "New York"
}

# Accessing values using keys
print("Name:", student_info["Name"])
print("Age:", student_info["Age"])
print("City:", student_info["City"])

# Modifying values
student_info["Age"] = 26
student_info["Grade"] = "A"

# Printing the modified dictionary
print("Modified Dictionary:", student_info)

# Removing a key-value pair
del student_info["City"]

# Printing the final dictionary
print("Final Dictionary:", student_info)

Output:

Name: John
Age: 25
City: New York
Modified Dictionary: {'Name': 'John', 'Age': 26, 'City': 'New York', 'Grade': 'A'}
Final Dictionary: {'Name': 'John', 'Age': 26, 'Grade': 'A'}

In Python, dictionaries, lists, and tuples are three distinct data types, each with its own characteristics. Here's a comparison between a dictionary and a list or tuple:

1. Structure:

# Dictionary
student_info = {"Name": "John", "Age": 25, "City": "New York"}

# List
grades = [90, 85, 92, 88]

# Tuple
coordinates = (3, 5)

2. Purpose:

A dictionary is suitable for storing related key-value pairs. A list is used to store an ordered collection of items, and a tuple is an immutable ordered collection.

3. Mutability:

# Dictionaries are mutable
student_info["Age"] = 26

# Lists are mutable
grades[1] = 87

# Tuples are immutable; this will raise an error
coordinates[0] = 4

4. Syntax:

# Accessing dictionary values using keys
name = student_info["Name"]

# Accessing list elements using indices
grade = grades[1]

# Accessing tuple elements using indices
x = coordinates[0]

5. Examples:

# Adding a new key-value pair to a dictionary
student_info["Grade"] = "A"

# Appending an element to a list
grades.append(95)

# Concatenating tuples
new_coordinates = coordinates + (7, 2)

6. Output:

Dictionary: {'Name': 'John', 'Age': 26, 'City': 'New York', 'Grade': 'A'}
List: [90, 87, 92, 88, 95]
Tuple: (3, 5, 7, 2)