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from typing import Callable, Optional, TypeVar, cast
from reactivex import Observable, abc, compose
from reactivex import operators as ops
from reactivex.internal.exceptions import SequenceContainsNoElementsError
from reactivex.typing import Predicate
_T = TypeVar("_T")
def first_or_default_async_(
has_default: bool = False, default_value: Optional[_T] = None
) -> Callable[[Observable[_T]], Observable[_T]]:
def first_or_default_async(source: Observable[_T]) -> Observable[_T]:
def subscribe(
observer: abc.ObserverBase[_T],
scheduler: Optional[abc.SchedulerBase] = None,
):
def on_next(x: _T):
observer.on_next(x)
observer.on_completed()
def on_completed():
if not has_default:
observer.on_error(SequenceContainsNoElementsError())
else:
observer.on_next(cast(_T, default_value))
observer.on_completed()
return source.subscribe(
on_next, observer.on_error, on_completed, scheduler=scheduler
)
return Observable(subscribe)
return first_or_default_async
def first_or_default_(
predicate: Optional[Predicate[_T]] = None, default_value: Optional[_T] = None
) -> Callable[[Observable[_T]], Observable[_T]]:
"""Returns the first element of an observable sequence that
satisfies the condition in the predicate, or a default value if no
such element exists.
Examples:
>>> res = source.first_or_default()
>>> res = source.first_or_default(lambda x: x > 3)
>>> res = source.first_or_default(lambda x: x > 3, 0)
>>> res = source.first_or_default(None, 0)
Args:
source -- Observable sequence.
predicate -- [optional] A predicate function to evaluate for
elements in the source sequence.
default_value -- [Optional] The default value if no such element
exists. If not specified, defaults to None.
Returns:
A function that takes an observable source and reutrn an
observable sequence containing the first element in the
observable sequence that satisfies the condition in the
predicate, or a default value if no such element exists.
"""
if predicate:
return compose(ops.filter(predicate), ops.first_or_default(None, default_value))
return first_or_default_async_(True, default_value)
__all__ = ["first_or_default_", "first_or_default_async_"]
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