在Python中导航多维JSON数组

Question

我正试图找出如何在Python中查询JSON数组。有人能告诉我如何做一个简单的搜索和打印通过一个相当复杂的数组请？

我使用的示例如下：http://eu.battle.net/api/wow/realm/status

例如，我想看看如何找到“Silvermoon”服务器，并打印出“population”，然后是“wintergrass”数组中的“controlling faction”。

数组片段当前如下所示：

{"type":"pve","population":"high","queue":false,"wintergrasp":{"area":1,"controlling-faction":0,"status":0,"next":1382350068792},"tol-barad":{"area":21,"controlling-faction":0,"status":0,"next":1382349141932},"status":true,"name":"Silvermoon","slug":"silvermoon","battlegroup":"Cyclone / Wirbelsturm","locale":"en_GB","timezone":"Europe/Paris"}

目前，我可以访问主数组，但似乎无法访问子数组，而不将整个内容复制到另一个新变量，这似乎是浪费。我希望能做些

import urllib2
import json

req = urllib2.Request("http://eu.battle.net/api/wow/realm/status", None, {})
opener = urllib2.build_opener()
f = opener.open(req)

x = json.load(f)  # open the file and read into a variable

# search and find the Silvermoon server
silvermoon_array = ????

# print the population
print silvermoon_array.????

# access the Wintergrasp sub-array
wintergrasp_sub = ????
print wintergrasp_sub.????  # print the controlling-faction variable

这将真正帮助我掌握如何访问其他东西。

Answer 1

Python的interactive mode是逐步探索结构化数据的好方法。很容易找到如何访问silvermoon服务器数据：

>>> data=json.load(urllib2.urlopen("http://eu.battle.net/api/wow/realm/status"))
>>> type(data)
<type 'dict'>
>>> data.keys()
[u'realms']
>>> type(data['realms'])
<type 'list'>
>>> type(data['realms'][0])
<type 'dict'>
>>> data['realms'][0].keys()
[u'status', u'wintergrasp', u'battlegroup', u'name', u'tol-barad', u'locale', u'queue', u'timezone', u'type', u'slug', u'population']
>>> data['realms'][0]['name']
u'Aegwynn'
>>> [realm['name'] for realm in data['realms']].index('Silvermoon')
212
>>> silvermoon= data['realms'][212]
>>> silvermoon['population']
u'high'
>>> type(silvermoon['wintergrasp'])
<type 'dict'>
>>> silvermoon['wintergrasp'].keys()
[u'status', u'next', u'controlling-faction', u'area']
>>> silvermoon['wintergrasp']['controlling-faction']
>>> silvermoon['population']
u'high'

如果你还不知道它们，你应该阅读dictionary.keys、list.index和list comprehensions来了解发生了什么。

在确定了数据的结构之后，您最终可以重写数据访问，使其更具可读性和效率：

realms= data['realms']
realm_from_name= dict( [(realm['name'], realm) for realm in realms])
print realm_from_name['Silvermoon']['population']
print realm_from_name['Silvermoon']['wintergrasp']['controlling-faction']

至于将数组复制到另一个变量是浪费，您应该知道python传递值by reference。这意味着当你给一个新变量赋值时不需要复制。Here's a simple explanation of passing by value vs passing by reference

最后，你似乎过分担心表现。Python的哲学是get it right first, optimize later。当工作正常时，如果需要更好的性能，则优化它（如果值得的话）。

Answer 2

这就是你想要的：

# -*- coding: utf-8 -*-
import json
import urllib2

def searchListOfDicts(listOfDicts, attr, value):
    """
    Loops through a list of dictionaries and returns matching attribute value pair
    You can also pass it slug, silvermoon or type, pve
    returns a list containing all matching dictionaries 
    """
    matches = [record for record in listOfDicts if attr in record and record[attr] == value]
    return matches

def myjsonDict():
    """
    Opens url, grabs json and puts it inside a dictionary
    """
    req = urllib2.Request("http://eu.battle.net/api/wow/realm/status", None, {})
    opener = urllib2.build_opener()
    f = opener.open(req)
    json_dict = json.load(f)
    return json_dict

jsonDict = myjsonDict()
#we want to search inside realms list
silverMoonServers = searchListOfDicts(jsonDict["realms"], "name", "Silvermoon")
#access first dictionary that matched "name, Silvermoon" query
print silverMoonServers[0]
print silverMoonServers[0]["wintergrasp"]
print silverMoonServers[0]["wintergrasp"]["controlling-faction"]

Answer 3

在Python中，json.loads将json对象映射到Python字典，并将Arrays映射到list，因此可以像使用常规Python dict和list结构一样执行进一步的操作。

以下是如何使用requests和lamdbas来完成此任务：

    import json
    import requests

    response = requests.get("http://eu.battle.net/api/wow/realm/status")
    json_data = json.loads(response.text)

    # loop through the list of realms to find the one you need (realm_name)
    get_realm = lambda realm_name, jd: [r for r in jd['realms'] 
                                        if r['name'] == realm_name]

    # extract data you need, if there is a match in the list of realms,
    # return None otherwise
    get_your_data = lambda realm: (
        realm[0]['name'],
        realm[0]['wintergrasp']['controlling-faction']
    ) if realm else None

    print get_your_data(get_realm('Silvermoon', json_data))