typing-extensions

Common errors

Warnings

Install

Install compatibility verified last tested: 2026-05-12

Imports

• TypedDict
  wrong

  from typing import TypedDict

  correct

  from typing_extensions import TypedDict

  typing_extensions version has additional features (ReadOnly, closed/extra_items via PEP 728) and bug fixes not present in the stdlib version on older Python releases. Prefer typing_extensions.TypedDict when targeting <3.13 for full feature parity.

• Annotated

  from typing_extensions import Annotated

  Safe to import from typing_extensions on all supported versions; re-exported from stdlib typing internally.

• Protocol
  wrong

  from typing import Protocol

  correct

  from typing_extensions import Protocol

  typing_extensions.Protocol has backported isinstance() fixes and allows @runtime_checkable interop. On Python <3.12 the stdlib version has known isinstance() performance and correctness issues.

• Self

  from typing_extensions import Self

  Backport of PEP 673; available in stdlib typing only from Python 3.11.

• TypeAlias

  from typing_extensions import TypeAlias

  Backport of PEP 613; in stdlib from Python 3.10. Use typing_extensions version for Python 3.9 compatibility.

• TypeAliasType

  from typing_extensions import TypeAliasType

  Backport of PEP 695 type alias syntax; native only in Python 3.12+.

• TypeGuard

  from typing_extensions import TypeGuard

  Backport of PEP 647; in stdlib from Python 3.10. Consider TypeIs (PEP 742, 4.10+) for more intuitive narrowing semantics.

• TypeIs

  from typing_extensions import TypeIs

  Added in 4.10.0 (PEP 742). Prefer over TypeGuard for most narrowing use-cases — TypeIs has stricter but more predictable semantics.

• override

  from typing_extensions import override

  Backport of PEP 698; in stdlib from Python 3.12. Decorator sets .__override__ = True at runtime.

• deprecated

  from typing_extensions import deprecated

  Backport of PEP 702 (added in 4.5.0). Raises DeprecationWarning at call site. Was a common ImportError source when frameworks (FastAPI, Pydantic) required >=4.8.0 but environments had older pinned versions.

• get_annotations

  from typing_extensions import get_annotations

  Added in 4.13.0. Backport of inspect.get_annotations with PEP 649 features. Do not use inspect.get_annotations directly if you need PEP 649 lazy evaluation semantics.

• evaluate_forward_ref

  from typing_extensions import evaluate_forward_ref

  Added in 4.13.0. Use instead of typing.get_type_hints() when you need fine-grained ForwardRef evaluation control under PEP 649.

• Buffer
  wrong

  from typing import ByteString

  correct

  from typing_extensions import Buffer

  typing.ByteString is deprecated and removed in Python 3.14. Use typing_extensions.Buffer for buffer-protocol types instead.

• LiteralString

  from typing_extensions import LiteralString

  Backport of PEP 675; in stdlib from Python 3.11.

• Never

  from typing_extensions import Never

  Backport of typing.Never (3.11+). Prefer over NoReturn for non-return-type positions.

Quickstart verified last tested: 2026-04-23

Demonstrates the most commonly used constructs: TypedDict with ReadOnly/NotRequired fields, TypeAlias, Self, runtime_checkable Protocol, TypeIs narrowing, the @deprecated decorator, and @override.

from typing_extensions import (
    TypedDict,
    NotRequired,
    ReadOnly,
    Annotated,
    Self,
    TypeAlias,
    override,
    deprecated,
    TypeIs,
    Protocol,
    runtime_checkable,
)
import sys

# TypedDict with optional and read-only fields (PEP 655, PEP 705)
class Movie(TypedDict):
    title: ReadOnly[str]
    year: NotRequired[int]

movie: Movie = {"title": "Blade Runner"}

# TypeAlias for clarity
Vector: TypeAlias = list[float]

# Self in method signatures
class Builder:
    def set_name(self, name: str) -> Self:
        self.name = name
        return self

# Protocol with runtime checking
@runtime_checkable
class Drawable(Protocol):
    def draw(self) -> None: ...

# TypeIs for narrowing
def is_str_list(val: list[object]) -> TypeIs[list[str]]:
    return all(isinstance(x, str) for x in val)

# deprecated decorator
@deprecated("Use new_api() instead")
def old_api() -> None:
    pass

# override for subclass safety
class Base:
    def compute(self) -> int:
        return 0

class Child(Base):
    @override
    def compute(self) -> int:
        return 42

print(f"typing_extensions quickstart OK — Python {sys.version}")