jsonfinder lets you find and extract JSON objects and arrays embedded within a string using a simple iterator. For example:

>>> s = 'jack [1,2,3] john'
>>> for start, end, obj in jsonfinder(s):
...     print start, ':', end
...     if obj is None:
...         print 'String:', repr(s[start:end])
...     else:
...         print 'List of length', len(obj)
0 : 5
String: 'jack '
5 : 12
List of length 3
12 : 17
String: ' john'
>>> assert len(s) == end

Two other convenience methods are also provided: has_json and only_json:

>>> has_json('stuff {"key": "value"} things')
True
>>> has_json('stuff only')
False
>>> only_json('stuff {"key": "value"} things')[2]
{u'key': u'value'}
>>> only_json('stuff only')
Traceback (most recent call last):
...
ValueError: No JSON object found in argument.
>>> only_json('{}{}')
Traceback (most recent call last):
...
ValueError: More than one JSON object found in the argument.

All the methods allow a custom JSONDecoder to be passed in for flexibility.

The library also includes a command-line tool to format JSON and filter out parts of the input based on whether JSON is present. It's like a more flexible version of python's built in json.tool, a grep -v for JSON, and more. For example:

$ cat cli_example.txt
This line contains no JSON and will be deleted by the --delete other-lines option.
On the other hand {"json":   ["is", "formatted"]  } and text surrounding it is preserved (but can also be removed if desired).
$ jsonfinder -i cli_example.txt --delete other-lines
On the other hand {
    "json": [
        "is",
        "formatted"
    ]
} and text surrounding it is preserved (but can also be removed if desired).
$ jsonfinder -i cli_example.txt --delete other-lines | jsonfinder --delete context --format tiny
{"json":["is","formatted"]}

See the --help option in the command-line for more details.

Installation is as simple as:

pip install jsonfinder