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from asyncio import Future
from typing import Callable, Optional, TypeVar, Union
from reactivex import Observable, abc, from_future, throw
from reactivex.scheduler import ImmediateScheduler
_T = TypeVar("_T")
def defer_(
factory: Callable[[abc.SchedulerBase], Union[Observable[_T], "Future[_T]"]]
) -> Observable[_T]:
"""Returns an observable sequence that invokes the specified factory
function whenever a new observer subscribes.
Example:
>>> res = defer(lambda scheduler: of(1, 2, 3))
Args:
observable_factory: Observable factory function to invoke for
each observer that subscribes to the resulting sequence. The
factory takes a single argument, the scheduler used.
Returns:
An observable sequence whose observers trigger an invocation
of the given observable factory function.
"""
def subscribe(
observer: abc.ObserverBase[_T], scheduler: Optional[abc.SchedulerBase] = None
) -> abc.DisposableBase:
try:
result = factory(scheduler or ImmediateScheduler.singleton())
except Exception as ex: # By design. pylint: disable=W0703
return throw(ex).subscribe(observer)
result = from_future(result) if isinstance(result, Future) else result
return result.subscribe(observer, scheduler=scheduler)
return Observable(subscribe)
__all__ = ["defer_"]
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