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firestar5683
72 lines
2.5 KiB
Python
72 lines
2.5 KiB
Python
from typing import Callable, Optional, TypeVar, cast
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from reactivex import Observable, abc, compose
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from reactivex import operators as ops
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from reactivex.internal.exceptions import SequenceContainsNoElementsError
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from reactivex.typing import Predicate
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_T = TypeVar("_T")
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def first_or_default_async_(
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has_default: bool = False, default_value: Optional[_T] = None
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) -> Callable[[Observable[_T]], Observable[_T]]:
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def first_or_default_async(source: Observable[_T]) -> Observable[_T]:
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def subscribe(
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observer: abc.ObserverBase[_T],
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scheduler: Optional[abc.SchedulerBase] = None,
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):
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def on_next(x: _T):
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observer.on_next(x)
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observer.on_completed()
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def on_completed():
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if not has_default:
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observer.on_error(SequenceContainsNoElementsError())
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else:
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observer.on_next(cast(_T, default_value))
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observer.on_completed()
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return source.subscribe(
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on_next, observer.on_error, on_completed, scheduler=scheduler
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)
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return Observable(subscribe)
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return first_or_default_async
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def first_or_default_(
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predicate: Optional[Predicate[_T]] = None, default_value: Optional[_T] = None
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) -> Callable[[Observable[_T]], Observable[_T]]:
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"""Returns the first element of an observable sequence that
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satisfies the condition in the predicate, or a default value if no
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such element exists.
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Examples:
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>>> res = source.first_or_default()
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>>> res = source.first_or_default(lambda x: x > 3)
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>>> res = source.first_or_default(lambda x: x > 3, 0)
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>>> res = source.first_or_default(None, 0)
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Args:
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source -- Observable sequence.
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predicate -- [optional] A predicate function to evaluate for
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elements in the source sequence.
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default_value -- [Optional] The default value if no such element
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exists. If not specified, defaults to None.
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Returns:
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A function that takes an observable source and reutrn an
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observable sequence containing the first element in the
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observable sequence that satisfies the condition in the
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predicate, or a default value if no such element exists.
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"""
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if predicate:
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return compose(ops.filter(predicate), ops.first_or_default(None, default_value))
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return first_or_default_async_(True, default_value)
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__all__ = ["first_or_default_", "first_or_default_async_"]
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