# -*- coding: utf-8 -*-
from functools import wraps
def _wrap(left, right, error_handler, proxy_new_listener):
left_emit = left.emit
left_unwrap = getattr(left, "unwrap", None)
def wrapped_emit(event, *args, **kwargs):
left_handled = left._call_handlers(event, args, kwargs)
# Do it for the right side
if proxy_new_listener or event != "new_listener":
right_handled = right._call_handlers(event, args, kwargs)
right_handled = False
handled = left_handled or right_handled
# Use the error handling on ``error_handler`` (should either be
# ``left`` or ``right``)
if not handled:
error_handler._emit_handle_potential_error(event, args if args else None)
left.emit = left_emit
left.unwrap = left_unwrap
left.emit = left_emit
if hasattr(right, "unwrap"):
left.emit = wrapped_emit
left.unwrap = unwrap
_PROXY_NEW_LISTENER_SETTINGS = dict(
cls, underlying, error_handling="new", proxy_new_listener="forward", *args, **kwargs
"""A helper to create instances of an event emitter ``cls`` that inherits
event behavior from an ``underlying`` event emitter instance.
This is mostly helpful if you have a simple underlying event emitter
that you don't have direct control over, but you want to use that
event emitter in a new context - for example, you may want to ``uplift`` a
``BaseEventEmitter`` supplied by a third party library into an
``AsyncIOEventEmitter`` so that you may register async event handlers
in your ``asyncio`` app but still be able to receive events from the
underlying event emitter and call the underlying event emitter's existing
handlers. This trick will also often work for a deprecated
When called, ``uplift`` instantiates a new instance of ``cls``, passing
along any unrecognized arguments, and overwrites the ``emit`` method on
the ``underlying`` event emitter to also emit events on the new event
emitter and vice versa. In both cases, they return whether the ``emit``
method was handled by either emitter. Execution order prefers the event
emitter on which ``emit`` was called.
``uplift`` also adds an ``unwrap`` method to both instances, either of
which will unwrap both ``emit`` methods when called.
The ``error_handling`` flag can be configured to control what happens to
- 'new': Error handling for the new event emitter is always used and the
underlying library's non-event-based error handling is inert.
- 'underlying': Error handling on the underlying event emitter is always
used and the new event emitter can not implement non-event-based error
- 'neither': Error handling for the new event emitter is used if the
handler was registered on the new event emitter, and vice versa.
Tuning this option can be useful depending on how the underlying event
emitter does error handling. The default is 'new'.
The ``proxy_new_listener`` option can be configured to control how
``new_listener`` events are treated:
- 'forward': ``new_listener`` events are propagated from the underlying
- 'both': ``new_listener`` events are propagated as with other events.
- 'neither': ``new_listener`` events are only fired on their respective
event emitter to the new event emitter but not vice versa.
- 'backward': ``new_listener`` events are propagated from the new event
emitter to the underlying event emitter, but not vice versa.
Tuning this option can be useful depending on how the ``new_listener``
event is used by the underlying event emitter, if at all. The default is
'forward', since ``underlying`` may not know how to handle certain
handlers, such as asyncio coroutines.
Each event emitter tracks its own internal table of handlers.
``remove_listener``, ``remove_all_listeners`` and ``listeners`` all
work independently. This means you will have to remember which event
emitter an event handler was added to!
Note that both the new event emitter returned by ``cls`` and the
underlying event emitter should inherit from ``BaseEventEmitter``, or at
least implement the interface for the undocumented ``_call_handlers`` and
) = _PROXY_NEW_LISTENER_SETTINGS[proxy_new_listener]
new = cls(*args, **kwargs)
uplift_error_handlers = dict(
new=(new, new), underlying=(underlying, underlying), neither=(new, underlying)
new_error_handler, underlying_error_handler = uplift_error_handlers[error_handling]
_wrap(new, underlying, new_error_handler, new_proxy_new_listener)
_wrap(underlying, new, underlying_error_handler, underlying_proxy_new_listener)