Lesson 9: Dictionaries & Sets

1. Dictionaries – Key-Value Pairs

Dictionaries store data in key:value pairs — like a real dictionary (word → definition).

Very useful in ML for storing hyperparameters, model configs, or data mappings.

student = {
    "name": "Alex",
    "age": 22,
    "grade": "A",
    "skills": ["Python", "ML"]
}
print(student["name"])  # Alex

Keys must be unique and immutable (strings, numbers, tuples).

2. Common Dictionary Methods

• .get(key, default) — safe access
• .keys() / .values() / .items()
• .update(other_dict)
• .pop(key)
• .clear()

Example:

model = {"type": "CNN", "layers": 5}
model.get("optimizer", "Adam")  # Adam (default if missing)