Dictionaries

A dictionary stores data as key-value pairs, letting you access values by key instead of position. It's useful for structured data, like a user's name, age, or preferences.

Keys must be unique and immutable (strings, numbers, or tuples). Values can be any type — strings, numbers, lists, or even other dictionaries.

Creating a Dictionary

Dictionaries are defined with curly braces, using key: value pairs separated by commas.

Example: person = {"name": "Alice", "age": 30} Here "name" maps to "Alice", and "age" maps to 30.

Accessing and Updating Values

Use square brackets to access a value: person["name"].

• If the key exists, it returns the value;
• If not, Python raises a KeyError.

With .get(), missing keys return None or a fallback: person.get("nickname", "N/A").

Update values by reassigning: person["age"] = 31.

Adding and Removing Items

To add a new key-value pair, just assign to a new key — Python will insert it: person["city"] = "London".

To remove a key, you can use del, as del person["age"]. Or use .pop("key") if you want to remove and return the value.

Keys and Values

Dictionaries come with handy built-in methods:

• .keys() returns a list-like view of all the keys;
• .values() returns all the values;
• .items() returns pairs as tuples — useful for looping.

These are especially useful when you're iterating or analyzing a dictionary.

Summary

• A dictionary holds key-value pairs, where keys are unique and used to look things up;
• Keys must be immutable (like strings or numbers), values can be any type;
• You can add, update, delete, and safely retrieve values using .get();
• Use .keys(), .values(), and .items() to work with dictionary content efficiently.