Create compact JSON with Python
Calling json.dumps(…, separators=(',', ':'))
will reduce the amount of whitespace in the final string.
To create compact JSON in Python:
>>> json.dumps({'a': 1, 'b': 2})
'{"a": 1, "b": 2}'
>>> json.dumps({'a': 1, 'b': 2}, separators=(',', ':'))
'{"a":1,"b":2}'
(via Raymond Hettinger)