5 4 Dictionaries Explained

Key Concepts

Dictionaries in Python are unordered collections of key-value pairs. The key concepts include:

• Creating Dictionaries
• Accessing Values
• Modifying Dictionaries
• Dictionary Methods
• Dictionary Comprehensions

1. Creating Dictionaries

Dictionaries are created using curly braces {} with key-value pairs separated by colons. Each key-value pair is separated by a comma.

Example:

student_scores = {
    "Alice": 90,
    "Bob": 85,
    "Charlie": 92
}
    

2. Accessing Values

Values in a dictionary are accessed using their keys. This can be done using square brackets [] with the key inside.

Example:

student_scores = {
    "Alice": 90,
    "Bob": 85,
    "Charlie": 92
}
print(student_scores["Alice"])  # Output: 90
    

Analogy: Think of a dictionary as a phone book where each name (key) has a corresponding phone number (value).

3. Modifying Dictionaries

Dictionaries are mutable, meaning you can change their content. You can add new key-value pairs, update existing values, or remove key-value pairs.

Example:

student_scores = {
    "Alice": 90,
    "Bob": 85,
    "Charlie": 92
}
student_scores["Alice"] = 95
student_scores["David"] = 88
del student_scores["Bob"]
print(student_scores)  # Output: {'Alice': 95, 'Charlie': 92, 'David': 88}
    

4. Dictionary Methods

Python provides several built-in methods to manipulate dictionaries. Some common methods include keys(), values(), items(), and get().

Example:

student_scores = {
    "Alice": 90,
    "Bob": 85,
    "Charlie": 92
}
print(student_scores.keys())  # Output: dict_keys(['Alice', 'Bob', 'Charlie'])
print(student_scores.values())  # Output: dict_values([90, 85, 92])
print(student_scores.items())  # Output: dict_items([('Alice', 90), ('Bob', 85), ('Charlie', 92)])
print(student_scores.get("Alice"))  # Output: 90
    

5. Dictionary Comprehensions

Dictionary comprehensions provide a concise way to create dictionaries. They are often used to apply an expression to each item in an existing iterable.

Example:

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

Putting It All Together

By understanding and using dictionaries effectively, you can store and manipulate collections of key-value pairs in Python. Dictionaries are a fundamental data structure that you will use frequently in your programming journey.

Example:

student_scores = {
    "Alice": 90,
    "Bob": 85,
    "Charlie": 92
}
student_scores["Alice"] = 95
student_scores["David"] = 88
del student_scores["Bob"]
print(student_scores.keys())  # Output: dict_keys(['Alice', 'Charlie', 'David'])
print(student_scores.values())  # Output: dict_values([95, 92, 88])
print(student_scores.items())  # Output: dict_items([('Alice', 95), ('Charlie', 92), ('David', 88)])
squares = {x: x**2 for x in range(5)}
print(squares)  # Output: {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}