typing-patterns

Python Typing Patterns

Python type annotation patterns without type: ignore. Always the correct solution.

Triggers

Use this skill when the user:

• Gets mypy/pyright errors
• Asks about Python type annotations
• Wants to add type hints
• Works with generics, protocols, TypeVar

Main Principle: NEVER type: ignore

Every type error has a correct solution. type: ignore is:

• Masking potential bugs
• Disabling type checking
• Technical debt

More details: ${CLAUDE_PLUGIN_ROOT}/skills/typing-patterns/references/why-no-type-ignore.md

Dictionary Typing — TypedDict Instead of dict

More details: ${CLAUDE_PLUGIN_ROOT}/skills/typing-patterns/references/dict-typing.md

# Bad: Weak level
def process(data: dict): ...

# Warning: Medium level
def process(data: dict[str, Any]): ...

# Good: Strong level
class UserData(TypedDict):
    id: int
    email: str
    name: str

def process(data: UserData): ...

Why TypedDict is better:

• Key checking at compile time (data["emial"] → error)
• Value type checking
• IDE autocomplete
• Data structure documentation

When dict[K, V] is acceptable:

• Homogeneous collections: dict[str, User], dict[int, float]
• Caches, counters, ID → object mappings

Basic Types (Python 3.10+)

# Primitives
x: int = 1
y: str = "hello"
z: bool = True
f: float = 1.5

# Collections (built-in)
items: list[str] = ["a", "b"]
mapping: dict[str, int] = {"a": 1}
unique: set[int] = {1, 2, 3}
pair: tuple[int, str] = (1, "a")

# Union (Python 3.10+)
value: int | str = 1
optional: str | None = None

# Callable
from collections.abc import Callable
handler: Callable[[int, str], bool] = lambda x, s: True

Generics

More details: ${CLAUDE_PLUGIN_ROOT}/skills/typing-patterns/references/generics.md

from typing import TypeVar, Generic

T = TypeVar("T")
K = TypeVar("K")
V = TypeVar("V")


class Repository(Generic[T]):
    def get(self, id: int) -> T | None: ...
    def save(self, item: T) -> T: ...


# Usage
class UserRepository(Repository[User]):
    pass


# Python 3.12+ syntax
class Repository[T]:
    def get(self, id: int) -> T | None: ...