Introduction to Dictionaries

Dictionaries in Python are collections of key-value pairs. They allow you to store and retrieve data efficiently using keys.

In this lesson, you’ll learn how to create, manipulate, and iterate over dictionaries.

Creating Dictionaries

A dictionary is created using curly braces {}, with key-value pairs separated by colons:

# Creating a dictionary
person = {"name": "Alice", "age": 25}
print(person)

Accessing Values

You can access a value in a dictionary using its key:

# Accessing values in a dictionary
person = {"name": "Alice", "age": 25}
print(person["name"])  # Outputs: Alice

Adding and Updating Key-Value Pairs

You can add or update key-value pairs in a dictionary:

# Adding and updating key-value pairs
person = {"name": "Alice"}
person["age"] = 25  # Adding a new key-value pair
person["name"] = "Bob"  # Updating an existing key
print(person)

Removing Key-Value Pairs

You can remove items from a dictionary using the del keyword or the pop() method:

# Removing items from a dictionary
person = {"name": "Alice", "age": 25}
del person["age"]
print(person)  # Outputs: {'name': 'Alice'}

Iterating Over Dictionaries

You can iterate over keys, values, or key-value pairs in a dictionary:

# Iterating over a dictionary
person = {"name": "Alice", "age": 25}
for key, value in person.items():
    print(f"{key}: {value}")

Using Dictionary Methods

Dictionaries come with useful methods: 

• keys(): Returns all keys. 
• values(): Returns all values. 
• items(): Returns key-value pairs.

# Dictionary methods
person = {"name": "Alice", "age": 25}
print(person.keys())  # Outputs: dict_keys(['name', 'age'])

Common Mistakes with Dictionaries

Here are some mistakes to avoid:

• Using mutable types (like lists) as keys in a dictionary (raises an error).
• Trying to access a non-existent key without using get().
• Overwriting an existing key unintentionally.

What Did We Learn?

In this lesson, you learned:

• How to create and manipulate dictionaries in Python.
• How to add, update, and remove key-value pairs.
• How to iterate over dictionaries and use their methods.

Great job! Let’s move to the next topic.