extract from json

[Kev Dwyer]

teddybubu at gmail.com wrote:

> I can't find any example on how to do this.
> I have a json file like so:
> {"bostock":
[{"url":"http://bl.ocks.org/mbostock/9360565","title":"titleplaceholder","date":"dateplaceholder"},
> 
{"url":"http://bl.ocks.org/mbostock/9265674","title":"titleplaceholder","date":"dateplaceholder"},
> 
{"url":"http://bl.ocks.org/mbostock/9265467","title":"titleplaceholder","date":"dateplaceholder"},
> 
{"url":"http://bl.ocks.org/mbostock/9234731","title":"titleplaceholder","date":"dateplaceholder"},
> 
{"url":"http://bl.ocks.org/mbostock/9232962","title":"titleplaceholder","date":"dateplaceholder"},
> 
> this goes on for more than 700 entries. only thing unique is the number at
> the end of the url. I am going to load the url in python, get the date and
> title and write it in the json itself. Right now I am stuck on just
> reading the url in the json. Here is my code:
> 
> import json
> 
> with open("bostock.json") as json_file:
>     json_data = json.load(json_file)
>     print(json_data)
> 
> I have tried json_data[0], json_data.url and a few others I forget right
> now and it does not seem to work.
> 
> I have already figured out how to get the title and date.
> First things first: How can i just get the url for each line of the above
> json file?


Hello 

Try:

Python 2.7.2 (default, Aug 19 2011, 20:41:43) [GCC] on linux2                                                           
Type "help", "copyright", "credits" or "license" for more information.                                                  

>>> import  json
>>> with open('/tmp/bostock.json') as f:
...     json_data = json.load(f)
... 
>>> json_data
{u'bostock': [{u'url': u'http://bl.ocks.org/mbostock/9360565', u'date': 
u'dateplaceholder', u'title': u'titleplaceholder'}, {u'url': 
u'http://bl.ocks.org/mbostock/9265674', u'date': u'dateplaceholder', 
u'title': u'titleplaceholder'}, {u'url': 
u'http://bl.ocks.org/mbostock/9265467', u'date': u'dateplaceholder', 
u'title': u'titleplaceholder'}, {u'url': 
u'http://bl.ocks.org/mbostock/9234731', u'date': u'dateplaceholder', 
u'title': u'titleplaceholder'}, {u'url': 
u'http://bl.ocks.org/mbostock/9232962', u'date': u'dateplaceholder', 
u'title': u'titleplaceholder'}]}

>>> urls = [x['url'] for x in json_data['bostock']]
>>> urls
[u'http://bl.ocks.org/mbostock/9360565', 
u'http://bl.ocks.org/mbostock/9265674', 
u'http://bl.ocks.org/mbostock/9265467', 
u'http://bl.ocks.org/mbostock/9234731', 
u'http://bl.ocks.org/mbostock/9232962']

Python loads the json in the file into a dictionary.  In this case, the 
dictionary has a single key, 'bostock', and the value in the dictionary for 
that key is a list (of dictionaries).  

To get the urls, you need to get the list 

json_data['bostock']

 and then iterate over it's elements, getting the value for the key url for 
each one.  
This is what the list comprehension 

[x['url'] for x in json_data['bostock']]

does.

I hope that helps,

Kev