singleton-decorator.py

from functools import wraps
import inspect


def singleton(func):
    @wraps(func)
    def decorator():
        if not hasattr(func, "instance"):
            func.instance = func()
        return func.instance

    @wraps(func)
    async def async_decorator():
        if not hasattr(func, "instance"):
            func.instance = await func()
        return func.instance

    if inspect.iscoroutinefunction(func):
        return async_decorator

    return decorator