> ## Documentation Index > Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt > Use this file to discover all available pages before exploring further. # Python TypedDict `TypedDict` is a type hint construct from the `typing` module used to specify the expected types of values associated with specific string keys in a dictionary. It provides structural type information to static type checkers (such as `mypy` or `pyright`) without altering the runtime behavior of the dictionary. At runtime, an instance of a `TypedDict` is a standard Python `dict`, and no type validation or enforcement occurs. ## Syntax `TypedDict` can be defined using two syntaxes: the class-based syntax (preferred for readability) and the alternative assignment syntax (required when dictionary keys are not valid Python identifiers or are reserved keywords). ```python theme={"dark"} from typing import TypedDict # Class-based syntax class Point2D(TypedDict): x: int y: int label: str # Alternative assignment syntax Point3D = TypedDict('Point3D', {'x': int, 'y': int, 'z': int, 'in-bounds': bool}) ``` ## Runtime Behavior `TypedDict` is strictly a static typing tool subject to type erasure. Instantiating a `TypedDict` creates a standard dictionary. It does not enforce types, restrict extra keys, or provide default values during execution. ```python theme={"dark"} # Static type checkers will flag the incorrect type for 'y' and the missing 'label'. # However, the Python interpreter will execute this without raising an exception. p: Point2D = {'x': 10, 'y': 'twenty'} print(type(p)) # Output: ``` ## Totality and Key Presence By default, a `TypedDict` is **total**, meaning every key defined in the type definition must be present in the dictionary instance. You can modify this behavior at the class level using the `total` parameter, or at the granular key level using `Required` and `NotRequired` (introduced in Python 3.11 via PEP 655). ### Class-Level Totality Setting `total=False` makes all keys in the dictionary optional. ```python theme={"dark"} class Config(TypedDict, total=False): timeout: int retries: int # Valid: Neither key is strictly required by the type checker c: Config = {} ``` ### Key-Level Totality (Python 3.11+) `NotRequired` marks specific keys as optional within a total `TypedDict`. Conversely, `Required` marks specific keys as mandatory within a non-total (`total=False`) `TypedDict`. ```python theme={"dark"} from typing import TypedDict, NotRequired, Required class User(TypedDict): username: str email: str bio: NotRequired[str] # Optional key class PartialUpdate(TypedDict, total=False): username: str email: str id: Required[int] # Mandatory key ``` ## Inheritance `TypedDict` supports multiple inheritance, allowing the composition of complex dictionary types from simpler ones. A subclass inherits all key-type pairs from its base classes. If multiple base classes define the same key, the type annotations for that key must match exactly, otherwise static type checkers will report a conflict. ```python theme={"dark"} class BaseItem(TypedDict): id: int name: str class PhysicalItem(BaseItem): weight_kg: float # PhysicalItem structurally expects: {'id': int, 'name': str, 'weight_kg': float} item: PhysicalItem = {'id': 101, 'name': 'Anvil', 'weight_kg': 45.5} ```

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