70 lines
2.0 KiB
Python
70 lines
2.0 KiB
Python
from typing import Optional, TypeVar, cast
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from .. import abc
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from ..disposable import Disposable
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from .innersubscription import InnerSubscription
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from .subject import Subject
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_T = TypeVar("_T")
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class BehaviorSubject(Subject[_T]):
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"""Represents a value that changes over time. Observers can
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subscribe to the subject to receive the last (or initial) value and
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all subsequent notifications.
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"""
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def __init__(self, value: _T) -> None:
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"""Initializes a new instance of the BehaviorSubject class which
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creates a subject that caches its last value and starts with the
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specified value.
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Args:
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value: Initial value sent to observers when no other value has been
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received by the subject yet.
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"""
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super().__init__()
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self.value: _T = value
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def _subscribe_core(
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self,
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observer: abc.ObserverBase[_T],
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scheduler: Optional[abc.SchedulerBase] = None,
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) -> abc.DisposableBase:
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with self.lock:
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self.check_disposed()
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if not self.is_stopped:
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self.observers.append(observer)
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observer.on_next(self.value)
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return InnerSubscription(self, observer)
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ex = self.exception
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if ex:
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observer.on_error(ex)
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else:
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observer.on_completed()
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return Disposable()
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def _on_next_core(self, value: _T) -> None:
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"""Notifies all subscribed observers with the value."""
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with self.lock:
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observers = self.observers.copy()
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self.value = value
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for observer in observers:
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observer.on_next(value)
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def dispose(self) -> None:
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"""Release all resources.
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Releases all resources used by the current instance of the
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BehaviorSubject class and unsubscribe all observers.
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"""
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with self.lock:
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self.value = cast(_T, None)
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super().dispose()
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