Python元编程动态属性和特性

Posted 2020-10-13

#19.1 使用动态属性转换数据
"""
#栗子19-2 osconfeed.py：下载 osconfeed.json
from urllib.request import urlopen
import os
import warnings
import json
import sys

URL = ‘http://www.oreilly.com/pub/sc/osconfeed‘
JSON = ‘data/osconfeed.json‘

path = os.path.join(sys.path[0],JSON)
path = path.replace(‘\\‘,‘/‘)


def load():
    if not os.path.exists(path):
        msg = ‘downloading {} to {}‘.format(URL,path)
        warnings.warn(msg)
        with urlopen(URL) as remote,open(path,‘wb‘) as local:
            local.write(remote.read())

    with open(path,‘rb‘) as fp:

        return json.load(fp)

feed = load()
print(sorted(feed[‘Schedule‘].keys()))  #[‘conferences‘, ‘events‘, ‘speakers‘, ‘venues‘]
for key,value in sorted(feed[‘Schedule‘].items()):
    print(‘{:3} {}‘.format(len(value),key))
‘‘‘
  1 conferences
494 events
357 speakers
 53 venues
 ‘‘‘
print(feed[‘Schedule‘][‘speakers‘][-1][‘name‘])  #Carina C. Zona
print(feed[‘Schedule‘][‘speakers‘][-1][‘serial‘]) #141590
print(feed[‘Schedule‘][‘events‘][40][‘name‘])     #There *Will* Be Bugs
print(feed[‘Schedule‘][‘events‘][40][‘speakers‘]) #[3471, 5199]
"""

#栗子19-5  通过“点儿”来调用属性
from urllib.request import urlopen
import os
import warnings
import json
import sys

URL = ‘http://www.oreilly.com/pub/sc/osconfeed‘
JSON = ‘data/osconfeed.json‘

path = os.path.join(sys.path[0],JSON)
path = path.replace(‘\\‘,‘/‘)


JSON1 = ‘data/osconfeed1.json‘

path1 = os.path.join(sys.path[0],JSON1)
path1 = path1.replace(‘\\‘,‘/‘)

def load():
    if not os.path.exists(path):
        msg = ‘downloading {} to {}‘.format(URL,path)
        warnings.warn(msg)
        with urlopen(URL) as remote,open(path,‘wb‘) as local:
            local.write(remote.read())

    with open(path1,‘rb‘) as fp:

        return json.load(fp)

from collections import abc
class FrozenJSON:
    def __init__(self, mapping):
        self.__data = dict(mapping)



    def __getattr__(self, name):
         if hasattr(self.__data, name):
             return getattr(self.__data, name)

         else:
             return FrozenJSON.build(self.__data[name])

    @classmethod
    def build(cls, obj):
        if isinstance(obj, abc.Mapping):
            return cls(obj)
        elif isinstance(obj, abc.MutableSequence):
            return [cls.build(item) for item in obj]
        else:
            return obj


raw_feed = load()
feed = FrozenJSON(raw_feed)
print(len(feed.Schedule.speakers))