notify_dict.py

import abc
import six


@six.add_metaclass(abc.ABCMeta)
class NotifyDict(dict):
    NOT_FOUND = object()

    @abc.abstractmethod
    def on_create(self, key, val):
        """Callback for new key assignment"""

    @abc.abstractmethod
    def on_delete(self, key, val):
        """Callback for key deletion"""

    @abc.abstractmethod
    def on_update(self, key, old, new):
        """Callback for key update"""

    def __delitem__(self, key):
        self.pop(key)

    def __setitem__(self, key, val):
        try:
            old = self[key]
        except KeyError:
            old = NotifyDict.NOT_FOUND
        finally:
            dict.__setitem__(self, key, val)
            if old is NotifyDict.NOT_FOUND:
                self.on_create(key, val)
            else:
                self.on_update(key, old, val)

    def copy(self):
        return type(self)(self)

    __copy__ = copy

    def update(self, d):
        for k, v in d.items():
            self[k] = v

    def clear(self):
        for k in self.keys():
            del self[k]

    def pop(self, key, *args):
        x = dict.pop(self, key, *args)
        self.on_delete(key, x)
        return x

    def popitem(self):
        k, v = dict.popitem(self)
        self.on_delete(k, v)
        return (k, v)

    def setdefault(self, key, default=None):
        try:
            return self[key]
        except KeyError:
            self[key] = default