FrozenJSON in Fluent Python

FrozenJSON.py

"""
explore2.py: Script to explore the OSCON schedule feed

    >>> from osconfeed import load
    >>> raw_feed = load()
    >>> feed = FrozenJSON(raw_feed)
    >>> len(feed.Schedule.speakers)
    357
    >>> sorted(feed.Schedule.keys())
    ['conferences', 'events', 'speakers', 'venues']
    >>> feed.Schedule.speakers[-1].name
    'Carina C. Zona'
    >>> talk = feed.Schedule.events[40]
    >>> talk.name
    'There *Will* Be Bugs'
    >>> talk.speakers
    [3471, 5199]
    >>> talk.flavor
    Traceback (most recent call last):
      ...
    KeyError: 'flavor'

"""

# BEGIN EXPLORE2
from collections import abc


class FrozenJSON:
    """A read-only façade for navigating a JSON-like object
       using attribute notation
    """

    def __new__(cls, arg):  # <1>
        if isinstance(arg, abc.Mapping):
            return super().__new__(cls)  # <2>
        elif isinstance(arg, abc.MutableSequence):  # <3>
            return [cls(item) for item in arg]
        else:
            return arg

    def __init__(self, mapping):
        self.__data = {}
        for key, value in mapping.items():
            if iskeyword(key):
                key += '_'
            self.__data[key] = value

    def __getattr__(self, name):
        if hasattr(self.__data, name):
            return getattr(self.__data, name)
        else:
            return FrozenJSON(self.__data[name])  # <4>
# END EXPLORE2

用于处理深层消息