Python 3.5 类型提示不会导致错误

Question

new features 之一在 Python 3.5 中是类型提示，灵感来自 mypy .

typing: PEP 484 – Type Hints.

我想测试它，但它没有按预期工作。

import typing

class BankAccount:
    def __init__(self, initial_balance: int = 0) -> None:
        self.balance = initial_balance
    def deposit(self, amount: int) -> None:
        self.balance += amount
    def withdraw(self, amount: int) -> None:
        self.balance -= amount
    def overdrawn(self) -> bool:
        return str(self.balance < 0)

my_account = BankAccount(15)
my_account.withdraw(5)
print(type(my_account.overdrawn()))

结果:

<class 'str'>

我预料到会出现错误，因为我期望 bool 作为返回类型。我在 Python 3.5 (docker) 和本地测试了它。我错过了什么，让它发挥作用吗？这种键入在运行时不起作用吗？

Answer 1

请参阅您链接到的 PEP 中摘要的第五段:

While these annotations are available at runtime through the usual __annotations__ attribute, no type checking happens at runtime . Instead, the proposal assumes the existence of a separate off-line type checker which users can run over their source code voluntarily