如何在字典和 google protobuf 枚举中使用类型提示？

Question

我正在尝试使用 protobuf 枚举作为字典中值的类型，但由于某种原因它不起作用。

我在 proto 中的枚举定义是：

enum Device {
  UNSPECIFIED = 0;
  ON = 1;
  OFF = 2;
}

编译导入成功后，如下代码报错

from devices_pb2 import Device

def foo(device: Device) -> Dict[str, Device]:
    pass

错误信息：

    def foo(device: Device) -> Dict[str, Device]:
  File "/home/ivan/anaconda3/envs/py37/lib/python3.7/typing.py", line 254, in inner
    return func(*args, **kwds)
  File "/home/ivan/anaconda3/envs/py37/lib/python3.7/typing.py", line 629, in __getitem__
    params = tuple(_type_check(p, msg) for p in params)
  File "/home/ivan/anaconda3/envs/py37/lib/python3.7/typing.py", line 629, in <genexpr>
    params = tuple(_type_check(p, msg) for p in params)
  File "/home/ivan/anaconda3/envs/py37/lib/python3.7/typing.py", line 142, in _type_check
    raise TypeError(f"{msg} Got {arg!r:.100}.")
TypeError: Parameters to generic types must be types. Got <google.protobuf.internal.enum_type_wrapper.EnumTypeWrapper object at 0x7f4df6d81850>.

但是，如果我不使用字典，那么它工作得很好：

def foo(device: Device) -> Device:
    pass

请问有没有办法解决这个问题？

Answer 1

添加以下内容解决了问题：

from __future__ import annotations

详情请查看here。

Answer 2

对于使用 Python 版本 < 3.7 的用户，添加引号应该有效：

from devices_pb2 import Device

def foo(device: 'Device') -> Dict[str, 'Device']:
    pass

如何在字典和 google protobuf 枚举中使用类型提示？

How to use type hinting with dictionaries and google protobuf enum?

python

enums

type-hinting

protocol-buffers