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pyobservable.py
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pyobservable.py
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from collections.abc import Hashable
from types import MethodType
from typing import Callable, Optional, Tuple, Any, Dict, Union, TypeVar
from weakref import WeakValueDictionary
EventHandlerMapping = WeakValueDictionary
Handler = TypeVar('Handler', bound=Callable)
class Observable:
__slots__ = '_event_mapping',
_event_mapping: Dict[Hashable, EventHandlerMapping]
def __new__(cls, *args, **kwargs):
instance = super(Observable, cls).__new__(cls)
event_mapping = {}
for c in cls.__mro__:
for event_key in getattr(c, '_events_', []):
if event_key in event_mapping:
raise ValueError(f'Duplicate event key: {event_key!r}')
else:
event_mapping[event_key] = EventHandlerMapping()
instance._event_mapping = event_mapping
return instance
def add_event(self, event_key: Hashable) -> None:
""""Adds an event to the list of possible events. Raise ValueError if the event key is already present."""
if event_key in self._event_mapping:
raise ValueError(f'Duplicate event key: {event_key!r}')
else:
self._event_mapping[event_key] = EventHandlerMapping()
def bind(self, event_key: Hashable, handler: Optional[Handler] = None) -> Union[Callable, Handler]:
"""Binds a handler function to the specified event. When handler is None, decorator usage is assumed."""
event_handlers = self._get_handler_mapping(event_key)
def bind(callback: Handler) -> Handler:
if not callable(callback):
raise TypeError('The provided object is not callable.')
k, v = self._compute_kv(callback)
event_handlers[k] = v
return callback
return bind if handler is None else bind(handler)
def unbind(self, event_key: Hashable, handler: Handler) -> None:
"""Removes the provided event handlers from the specified event."""
event_handlers = self._get_handler_mapping(event_key)
k = self._compute_kv(handler)[0]
try:
del event_handlers[k]
except KeyError:
raise ValueError(f'Handler was not found in event key {event_key!r}')
def unbind_all(self) -> None:
"""Clears all event handlers from all events."""
for event_handlers in self._event_mapping.values():
event_handlers.clear()
def notify(self, event_key: Hashable, *args, **kwargs) -> None:
"""Calls all bound event handlers with the entered arguments. Compatibility between the arguments and the
handler's function signature is not enforced."""
for k, v in self._get_handler_mapping(event_key).items():
func_name = k[0]
(v if func_name is None else getattr(v, func_name))(*args, **kwargs)
def _get_handler_mapping(self, event_key: Hashable) -> EventHandlerMapping:
try:
return self._event_mapping[event_key]
except KeyError:
raise ValueError(f'No such event key {event_key!r}')
@staticmethod
def _compute_kv(obj: Any) -> Tuple[Tuple[Optional[str], int], Any]:
if isinstance(obj, MethodType):
return (obj.__func__.__name__, id(obj.__self__)), obj.__self__
else:
return (None, id(obj)), obj