weakref_test.py

import weakref
#import click
import pyhf

__events = {}
def subscribe(event, func):
    global __events
    __events.setdefault(event, Callables()).append(func)

class Greet:
    def __init__(self, name):
        self.name = name
        subscribe('event', self.method)

    def method(self):
        print(f"{self.name} called!")

    def __del__(self):
        print(f"{self.name} dying!")

class WeakList(list):
    def append(self, item):
        list.append(self, weakref.WeakMethod(item, self.remove))

class Callables(WeakList):
    def __call__(self, *args, **kwargs):
        for func in self:
            # weakref: needs to be de-ref'd first before calling
            func()(*args, **kwargs)

    def __repr__(self):
        return "Callables(%s)" % list.__repr__(self)

items = []

for name in 'ABCDEFGHIJKLMNOPQRSTUVWXYZ':
    items.append(Greet(name))

del items[6:8]

for k,v in __events.items():
    v()