Elements are added to list using append():
>>> data = {'list': [{'a':'1'}]}
>>> data['list'].append({'b':'2'})
>>> data
{'list': [{'a': '1'}, {'b': '2'}]}
If you want to add element to a specific place in a list (i.e. to the beginning), use insert() instead:
>>> data['list'].insert(0, {'b':'2'})
>>> data
{'list': [{'b': '2'}, {'a': '1'}]}
After doing that, you can assemble JSON again from dictionary you modified:
>>> json.dumps(data)
'{"list": [{"b": "2"}, {"a": "1"}]}'