Python 3.14 Preview: Lazy Annotations

python-annotations/README.md

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+# Python 3.14 Preview: Lazy Annotations
+
+This folder contains sample code for the Real Python tutorial [Python 3.14 Preview: Lazy Annotations](https://realpython.com/python-annotations/).

python-annotations/calculator.pyi

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+type Number = int | float
+
+class Calculator:
+    history: list[Number]
+
+    def __init__(self) -> None: ...
+    def add(self, a: Number, b: Number) -> Number: ...
+
+def add(a: Number, b: Number) -> Number: ...

python-annotations/fib.py

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+from typing import Annotated
+
+
+def fib(n: int) -> int:
+    return n if n < 2 else fib(n - 2) + fib(n - 1)
+
+
+def increment(x: Annotated[int, fib(35)]) -> int:
+    return x + 1

python-annotations/forward_references_future.py

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+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Any, Optional
+
+
+@dataclass
+class LinkedList:
+    head: Node
+
+
+@dataclass
+class Node:
+    value: Any
+    next: Optional[Node] = None

python-annotations/forward_references_strings.py

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+from dataclasses import dataclass
+from typing import Any, Optional
+
+
+@dataclass
+class LinkedList:
+    head: "Node"
+
+
+@dataclass
+class Node:
+    value: Any
+    next: Optional["Node"] = None

python-annotations/linked_list.py

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+from dataclasses import dataclass
+from typing import Any, Optional
+
+
+@dataclass
+class LinkedList:
+    head: Node  # noqa
+
+
+@dataclass
+class Node:
+    value: Any
+    next: Optional[Node] = None  # noqa

python-annotations/models.py

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+from dataclasses import dataclass
+
+from validators import validate_email
+
+
+@dataclass
+class User:
+    email: str
+    password: str
+
+    def __post_init__(self):
+        validate_email(self)

python-annotations/requirements.txt

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+annotated-types==0.7.0
+dnspython==2.7.0
+email_validator==2.2.0
+idna==3.10
+polars==1.31.0
+pydantic==2.11.7
+pydantic_core==2.33.2
+typeguard==4.4.4
+typing-inspection==0.4.1
+typing_extensions==4.14.1

python-annotations/rtti.py

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+from typeguard import typechecked
+
+
+@typechecked
+def add(a: int, b: int) -> int:
+    return a + b

python-annotations/validators.py

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+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from models import User
+
+
+def validate_email(user: User):
+    if user.email is None:
+        raise ValueError("email is required")