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from __future__ import annotations
from typing import TYPE_CHECKING, Callable, Optional, TypeVar
from reactivex import abc
from reactivex.internal.basic import default_error, noop
from reactivex.typing import OnCompleted, OnError, OnNext
_T_in = TypeVar("_T_in", contravariant=True)
if TYPE_CHECKING:
from reactivex.notification import Notification
else:
class Notification:
pass
class Observer(abc.ObserverBase[_T_in], abc.DisposableBase):
"""Base class for implementations of the Observer class. This base
class enforces the grammar of observers where OnError and
OnCompleted are terminal messages.
"""
def __init__(
self,
on_next: Optional[OnNext[_T_in]] = None,
on_error: Optional[OnError] = None,
on_completed: Optional[OnCompleted] = None,
) -> None:
self.is_stopped = False
self._handler_on_next: OnNext[_T_in] = on_next or noop
self._handler_on_error: OnError = on_error or default_error
self._handler_on_completed: OnCompleted = on_completed or noop
def on_next(self, value: _T_in) -> None:
"""Notify the observer of a new element in the sequence."""
if not self.is_stopped:
self._on_next_core(value)
def _on_next_core(self, value: _T_in) -> None:
"""For Subclassing purpose. This method is called by `on_next()`
method until the observer is stopped.
"""
self._handler_on_next(value)
def on_error(self, error: Exception) -> None:
"""Notify the observer that an exception has occurred.
Args:
error: The error that occurred.
"""
if not self.is_stopped:
self.is_stopped = True
self._on_error_core(error)
def _on_error_core(self, error: Exception) -> None:
"""For Subclassing purpose. This method is called by `on_error()`
method until the observer is stopped.
"""
self._handler_on_error(error)
def on_completed(self) -> None:
"""Notifies the observer of the end of the sequence."""
if not self.is_stopped:
self.is_stopped = True
self._on_completed_core()
def _on_completed_core(self) -> None:
"""For Subclassing purpose. This method is called by `on_completed()`
method until the observer is stopped.
"""
self._handler_on_completed()
def dispose(self) -> None:
"""Disposes the observer, causing it to transition to the
stopped state."""
self.is_stopped = True
def fail(self, exn: Exception) -> bool:
if not self.is_stopped:
self.is_stopped = True
self._on_error_core(exn)
return True
return False
def throw(self, error: Exception) -> None:
import traceback
traceback.print_stack()
raise error
def to_notifier(self) -> Callable[[Notification[_T_in]], None]:
"""Creates a notification callback from an observer.
Returns the action that forwards its input notification to the
underlying observer."""
def func(notifier: Notification[_T_in]) -> None:
return notifier.accept(self)
return func
def as_observer(self) -> abc.ObserverBase[_T_in]:
"""Hides the identity of an observer.
Returns an observer that hides the identity of the specified
observer.
"""
return Observer(self.on_next, self.on_error, self.on_completed)
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