Dynamic binding

payment.py

def method_dispatch(func):
    dispatcher = functools.singledispatch(func)

    def wrapper(*args, **kw):
        return dispatcher.dispatch(args[1].__class__)(*args, **kw)

    wrapper.register = dispatcher.register
    functools.update_wrapper(wrapper, func)
    return wrapper

class Payment:
  # ... existing code
  
  @method_dispatch
  def apply(self, event: DomainEvent):
    raise ValueError('Unknown event!')

  @apply.register(PaymentCreated)
  def _(self, event: PaymentCreated):
    self._status = 'PENDING_PROCESSING'
    self._amount_due = event.amount_due
  
  def record_that(self, event: DomainEvent):
    self.apply(event)
    self.events.append(event)