Generating json in python for app engine

Question

I am somewhat new to python and I am wondering what the best way is to generate json in a loop. I could just mash a bunch of strings together in the loop, but I'm sure there is a better way. Here's some more specifics. I am using app engine in python to create a service that returns json as a response.

So as an example, let's say someone requests a list of user records from the service. After the service queries for the records, it needs to return json for each record it found. Maybe something like this:

{records: 
{record: { name:bob, email:[email protected], age:25 } },
{record: { name:steve, email:[email protected], age:30 } }, 
{record: { name:jimmy, email:[email protected], age:31 } }, 
}

Excuse my poorly formatted json. Thanks for your help.

I think you're overthinking this. There's a JSON library for Python, just generate the data structure and pass it to json.dumps — Michael Lorton
– Michael Lorton, Commented May 3, 2011 at 15:50

Ignacio Vazquez-Abrams · Accepted Answer · 2011-05-03 15:51:41Z

18

Creating your own JSON is silly. Use json or simplejson for this instead.

>>> json.dumps(dict(foo=42))
'{"foo": 42}'

answered May 3, 2011 at 15:51

Ignacio Vazquez-Abrams

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scum · Accepted Answer · 2011-05-03 16:17:40Z

7

My question is how do I add to the dictionary dynamically? So foreach record in my list of records, add a record to the dictionary.

You may be looking to create a list of dictionaries.

records = []
record1 = {"name":"Bob", "email":"[email protected]"}
records.append(record1)    
record2 = {"name":"Bob2", "email":"[email protected]"}
records.append(record2)

Then in app engine, use the code above to export records as json.

answered May 3, 2011 at 16:17

scum

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scum · Accepted Answer · 2011-05-03 15:56:47Z

4

Few steps here.

First import simplejson

from django.utils import simplejson

Then create a function that will return json with the appropriate data header.

def write_json(self, data):
  self.response.headers['Content-Type'] = 'application/json'
  self.response.out.write(simplejson.dumps(data))

Then from within your post or get handler, create a python dictionary with the desired data and pass that into the function you created.

 ret = {"records":{
   "record": {"name": "bob", ...}
   ...
 }
 write_json(self, ret)

answered May 3, 2011 at 15:56

scum

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2 Comments

Sam Over a year ago

My question is how do I add to the dictionary dynamically? So foreach record in my list of records, add a record to the dictionary.

msharp Over a year ago

as the original question specifically relates to appengine, it is worth noting that the django library is not automatically available. You need to include a reference to it in your app.yaml stackoverflow.com/questions/11174750/…

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