Basic Annotations (int, str, list)¶

Basic type annotations include primitive types and built-in collection types, forming the foundation of type hinting.

Primitive Type Annotations¶

Annotate variables with primitive types like int, str, float, and bool.

```python

Primitive types¶

name: str = "Alice" age: int = 30 height: float = 5.8 is_active: bool = True

print(f"{name}, {age}, {height}, {is_active}") ```

Alice, 30, 5.8, True

Collection Type Annotations¶

Annotate collections and specify their element types.

```python

Collection types (Python 3.9+)¶

numbers: list[int] = [1, 2, 3] tags: set[str] = {"python", "typing"} coords: tuple[float, float] = (10.5, 20.3)

Dictionaries with key-value types¶

config: dict[str, int] = {"port": 8080, "timeout": 30}

print(f"Numbers: {numbers}") print(f"Config: {config}") ```

Numbers: [1, 2, 3] Config: {'port': 8080, 'timeout': 30}

Function Annotations¶

Annotate function parameters and return types.

```python def add(a: int, b: int) -> int: return a + b

def greet(name: str) -> str: return f"Hello, {name}"

result1 = add(5, 3) result2 = greet("World") print(result1, result2) ```

8 Hello, World

Exercises¶

Exercise 1. Add type annotations to the following function and variable declarations:

```python def greet(name, times): for i in range(times): print(f"Hello, {name}!")

age = 25 scores = [90, 85, 92] active = True ```

Exercise 2. Write a function average(numbers: list[float]) -> float that returns the arithmetic mean. What happens if you pass an empty list? Add a docstring explaining the expected behavior.

Raises ZeroDivisionError if the list is empty.
"""
return sum(numbers) / len(numbers)

Exercise 3. Predict whether mypy would report an error for each line:

python x: int = "hello" y: str = 42 z: list[int] = [1, 2, 3] w: list[int] = [1, "two", 3]

Exercise 4. Annotate a function create_user(name: str, age: int, email: str) -> dict[str, str | int] and implement it. Then annotate a variable that stores the return value.