from __future__ import absolute_import

from abc import abstractmethod

try:
  from collections.abc import MutableMapping
except ImportError:
  from collections import MutableMapping


class DefaultMapping(MutableMapping):

  __slots__ = ()

  @abstractmethod
  def __contains__(self, key):  # pragma: nocover
    return False

  @abstractmethod
  def __getitem__(self, key):  # pragma: nocover
    if hasattr(self.__class__, '__missing__'):
      return self.__class__.__missing__(self, key)
    else:
      raise KeyError(key)

  def get(self, key, default=None):
    if key in self:
      return self[key]
    else:
      return default

  __marker = object()

  def pop(self, key, default=__marker):
    if key in self:
      value = self[key]
      del self[key]
    elif default is self.__marker:
      raise KeyError(key)
    else:
      value = default
    return value

  def setdefault(self, key, default=None):
    if key in self:
      value = self[key]
    else:
      self[key] = value = default
    return value


DefaultMapping.register(dict)
