a decorator of `maybe coroutine`

maybe_coroutine.py

from typing import Union, Callable, Generic, GenericMeta, TypeVar
from types import CoroutineType
from asyncio import iscoroutinefunction
from functools import wraps
from asyncio import coroutine
from typing import Callable, Any


MaybeCorouteine = Union[CoroutineType, Callable]
Handler = Callable[..., WsgiResponse]

MaybeType = Generic[TypeVar("Just"), TypeVar("Error")]
Maybe: GenericMeta = type("Maybe", (MaybeType, ), {})


def maybe_coroutine(fn: Callable) -> Callable[..., MaybeCorouteine]:
    if iscoroutinefunction(fn):
        return coroutine
    else:
        return lambda x: x


def maybe_async_cps(fn: Callable) -> MaybeCorouteine:

    def parted(context: Callable[[Maybe], Response]):
        @wraps(fn)
        @maybe_coroutine(fn)
        def _(*args, **kwargs):
            try:
                if iscoroutinefunction(fn):
                    result = yield from fn(*args, **kwargs)
                else:
                    result = fn(*args, **kwargs)
            except Exception as e:
                result = e
            return context(result)
        return _
    return parted