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import asyncio
import functools
from async_property.proxy import AwaitableOnly
is_coroutine = asyncio.iscoroutinefunction
def async_property(func, *args, **kwargs):
assert is_coroutine(func), 'Can only use with async def'
return AsyncPropertyDescriptor(func, *args, **kwargs)
class AsyncPropertyDescriptor:
def __init__(self, _fget, field_name=None):
self._fget = _fget
self.field_name = field_name or _fget.__name__
functools.update_wrapper(self, _fget)
def __set_name__(self, owner, name):
self.field_name = name
def __get__(self, instance, owner):
if instance is None:
return self
return self.awaitable_only(instance)
def __set__(self, instance, value):
raise ValueError(INVALID_ACTION.format('set'))
def __delete__(self, instance):
raise ValueError(INVALID_ACTION.format('delete'))
def get_loader(self, instance):
@functools.wraps(self._fget)
async def get_value():
return await self._fget(instance)
return get_value
def awaitable_only(self, instance):
return AwaitableOnly(self.get_loader(instance))
INVALID_ACTION = 'Cannot {} @async_property. ' \
'Use @async_cached_property instead.'
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