Mypy：注释函数，其中返回类型取决于参数的类型

Question

我有一个代表标准化内存量的类。

class MemoryUnit(enum.Enum):
    """Units of memory."""

    GB = 'GB'
    TB = 'TB'
    PB = 'PB'

class Memory(BaseModel):
    """Normalized amount of memory."""

    amount: int
    unit: MemoryUnit

现在我想为这个班级实现基本算术。加法、减法和乘法很容易注释：

def __add__(self, other: Memory) -> Memory: ...
def __sub__(self, other: Memory) -> Memory: ...
def __mul__(self, other: int) -> Memory: ...

不过，我对分裂有疑问。我看到除法的两个用例：

• 除以Memory并Memory得到 a float（两个存储量之间的比率是多少）。
• 除以Memory并int得到（如果均匀除以Memory的数量是多少）Memoryn

mypy 有没有办法用这个特定的签名来注释函数？

Answer 1

typing.overload允许您注册一个函数的多个不同签名。用 \xe2\x80\x94 修饰的函数@overload在运行时会被忽略，它们只是为了类型检查器的好处 \xe2\x80\x94 所以你可以将这些函数的主体留空。通常，您只需放置文字省略号...、文档字符串或pass在这些函数的正文中此外，您还需要确保该函数至少有一种具体实现可供在运行时使用。

\n

from typing import overload, Union\n\nclass Memory(BaseModel):\n    """Normalized amount of memory."""\n\n    amount: int\n    unit: MemoryUnit\n\n    def __add__(self, other: Memory) -> Memory: ...\n    def __sub__(self, other: Memory) -> Memory: ...\n    def __mul__(self, other: int) -> Memory: ...\n\n    @overload\n    def __div__(self, other: Memory) -> float:\n        """Signature of `Memory.__div__` if an instance of `Memory`\n        is divided by another instance of `Memory`\n        """\n\n    @overload\n    def __div__(self, other: int) -> Memory:\n        """Signature of `Memory.__div__` if an instance of `Memory`\n        is divided by an `int`\n        """\n\n    def __div__(self, other: Union[int, Memory]) -> Union[Memory, float]:\n        """[Your actual runtime implementation goes here]"""\n

\n