Python JSON encoding

Question

I'm trying to encode data to JSON in Python and I been having a quite a bit of trouble. I believe the problem is simply a misunderstanding.

I'm relatively new to Python and never really got familiar with the various Python data types, so that's most likely what's messing me up.

Currently I am declaring a list, looping through and another list, and appending one list within another:

import simplejson, json
data = [['apple', 'cat'], ['banana', 'dog'], ['pear', 'fish']]

x = simplejson.loads(data)
# >>> typeError: expected string or buffer..

x = simplejson.dumps(stream)
# >>> [["apple", "cat"], ["banana", "dog"], ["pear", "fish"]]
# - shouldn't JSON encoded strings be like: {{"apple":{"cat"},{"banana":"dog"}}

So I either:

• I don't understand JSON Syntax
• I don't understand the Pythons JSON module(s)
• I'm using an inappropriate data type.

Answer 1

Python lists translate to JSON arrays. What it is giving you is a perfectly valid JSON string that could be used in a Javascript application. To get what you expected, you would need to use a dict:

>>> json.dumps({'apple': 'cat', 'banana':'dog', 'pear':'fish'})
'{"pear": "fish", "apple": "cat", "banana": "dog"}'

Answer 2

I think you are simply exchanging dumps and loads.

>>> import json
>>> data = [['apple', 'cat'], ['banana', 'dog'], ['pear', 'fish']]

The first returns as a (JSON encoded) string its data argument:

>>> encoded_str = json.dumps( data )
>>> encoded_str
'[["apple", "cat"], ["banana", "dog"], ["pear", "fish"]]'

The second does the opposite, returning the data corresponding to its (JSON encoded) string argument:

>>> decoded_data = json.loads( encoded_str )
>>> decoded_data
[[u'apple', u'cat'], [u'banana', u'dog'], [u'pear', u'fish']]
>>> decoded_data == data
True

Answer 3

In simplejson (or the library json in Python 2.6 and later), loads takes a JSON string and returns a Python data structure, dumps takes a Python data structure and returns a JSON string. JSON string can encode Javascript arrays, not just objects, and a Python list corresponds to a JSON string encoding an array. To get a JSON string such as

{"apple":"cat", "banana":"dog"}

the Python object you pass to json.dumps could be:

dict(apple="cat", banana="dog")

though the JSON string is also valid Python syntax for the same dict. I believe the specific string you say you expect is simply invalid JSON syntax, however.