James
40 lines
1.1 KiB
Python
40 lines
1.1 KiB
Python
from typing import Callable, Optional, TypeVar, cast
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from reactivex import Observable, compose
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from reactivex import operators as ops
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from reactivex.typing import Predicate
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_T = TypeVar("_T")
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def single_(
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predicate: Optional[Predicate[_T]] = None,
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) -> Callable[[Observable[_T]], Observable[_T]]:
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"""Returns the only element of an observable sequence that satisfies the
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condition in the optional predicate, and reports an exception if there
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is not exactly one element in the observable sequence.
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Example:
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>>> res = single()
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>>> res = single(lambda x: x == 42)
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Args:
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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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Returns:
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An observable sequence containing the single element in the
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observable sequence that satisfies the condition in the predicate.
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"""
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if predicate:
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return compose(ops.filter(predicate), ops.single())
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else:
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return cast(
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Callable[[Observable[_T]], Observable[_T]],
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ops.single_or_default_async(False),
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)
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__all__ = ["single_"]
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