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from typing import Callable, Optional, Tuple, TypeVar, cast
from reactivex import Observable, abc
_T = TypeVar("_T")
def pairwise_() -> Callable[[Observable[_T]], Observable[Tuple[_T, _T]]]:
def pairwise(source: Observable[_T]) -> Observable[Tuple[_T, _T]]:
"""Partially applied pairwise operator.
Returns a new observable that triggers on the second and
subsequent triggerings of the input observable. The Nth
triggering of the input observable passes the arguments from
the N-1th and Nth triggering as a pair. The argument passed to
the N-1th triggering is held in hidden internal state until the
Nth triggering occurs.
Returns:
An observable that triggers on successive pairs of
observations from the input observable as an array.
"""
def subscribe(
observer: abc.ObserverBase[Tuple[_T, _T]],
scheduler: Optional[abc.SchedulerBase] = None,
) -> abc.DisposableBase:
has_previous = False
previous: _T = cast(_T, None)
def on_next(x: _T) -> None:
nonlocal has_previous, previous
pair = None
with source.lock:
if has_previous:
pair = (previous, x)
else:
has_previous = True
previous = x
if pair:
observer.on_next(pair)
return source.subscribe(on_next, observer.on_error, observer.on_completed)
return Observable(subscribe)
return pairwise
__all__ = ["pairwise_"]
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