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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 single_or_default_async_(
has_default: bool = False, default_value: Optional[_T] = None
) -> Callable[[Observable[_T]], Observable[_T]]:
def single_or_default_async(source: Observable[_T]) -> Observable[_T]:
def subscribe(
observer: abc.ObserverBase[_T],
scheduler: Optional[abc.SchedulerBase] = None,
):
value = cast(_T, default_value)
seen_value = False
def on_next(x: _T):
nonlocal value, seen_value
if seen_value:
observer.on_error(
Exception("Sequence contains more than one element")
)
else:
value = x
seen_value = True
def on_completed():
if not seen_value and not has_default:
observer.on_error(SequenceContainsNoElementsError())
else:
observer.on_next(value)
observer.on_completed()
return source.subscribe(
on_next, observer.on_error, on_completed, scheduler=scheduler
)
return Observable(subscribe)
return single_or_default_async
def single_or_default_(
predicate: Optional[Predicate[_T]] = None, default_value: _T = None
) -> Callable[[Observable[_T]], Observable[_T]]:
"""Returns the only element of an observable sequence that matches
the predicate, or a default value if no such element exists this
method reports an exception if there is more than one element in the
observable sequence.
Examples:
>>> res = single_or_default()
>>> res = single_or_default(lambda x: x == 42)
>>> res = single_or_default(lambda x: x == 42, 0)
>>> res = single_or_default(None, 0)
Args:
predicate -- [Optional] A predicate function to evaluate for
elements in the source sequence.
default_value -- [Optional] The default value if the index is
outside the bounds of the source sequence.
Returns:
An observable Sequence containing the single 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.single_or_default(None, default_value)
)
else:
return single_or_default_async_(True, default_value)
__all__ = ["single_or_default_", "single_or_default_async_"]
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