Introduction ¶

Python operates as a dynamically-typed language, meaning type-checking happens during execution rather than compilation, and variables can change types throughout their lifetime.

The article illustrates this with an example where 1 + "two" raises an error due to type incompatibility. Since PEP 484, Python has supported type-hints, enabling static type checking through tools like PyCharm or Mypy—though Python doesn’t enforce these hints by default.

Why Use Type Hints? ¶

Type hints enhance IDE functionality and linting capabilities, making code reasoning more straightforward for developers and tools alike.

Simple Type Hint ¶

Basic syntax: variable: type = value

def do_something(first_arg: int = 0, second_arg: str = ''):
    return first_arg * second_arg

a: int = 1
b: float = 1.0
c: bool = True
d: str = "test"
e: bytes = b"test"

Collection Type Hint ¶

Python 3.9+ ¶

a: list[int] = [1]
b: set[int] = {6, 7}
c: dict[str, int] = {'a': 1, 'b': 2}
d: tuple[int, int] = (1, 2)

Python < 3.9 ¶

Requires importing from the typing module:

from typing import List, Set, Dict, Tuple, Optional, Union, Any

a: List[int] = [1]
b: Set[int] = {6, 7}
c: Dict[str, int] = {'a': 1, 'b': 2}
d: Tuple[int, int] = (1, 2)
x: Tuple[int, ...] = (1, 2, 3, 4, 5)

Complex Type Hint ¶

a1: List[Union[int, str, bool]] = [False, 1, '1']
b2: Set[Any] = {2, True}
b4: Optional[Set[Any]] = None

class Animal():
    def __init__(self, name: str, sound: str):
        self.name: str = name
        self.sound: str = name

c2: Animal = 'test'

Checking Static Typing Using Mypy ¶

After installing Mypy, create a test file and run: mypy type_hints.py

Example with errors ¶

type_hints.py:11: error: Name 'a' already defined on line 10
Found 1 error in 1 file

The tool identifies 10 common type violations including mismatched collection elements, incorrect tuple assignments, and incompatible type assignments.

Conclusion ¶

Type hints improve both IDE assistance and code comprehension. Developers can experiment with various types, then incorporate Mypy to enforce static typing in Python projects.