Splitting String in python and convert to json

If the format is actually this specific, it's pretty easy: just split on the [, because there are no [ parts inside the {…}. So:

>>> s = """{'4': {1, 2}, '2': {1, 2}, '0': {1, 2}}["eq('2', '0')", "eq('2', '4')", "eq('0','4')"]"""
>>> sd, _, sl = s.partition('[')
>>> sl = '[' + sl

Now, presumably you don't want to convert the string to JSON, but the dict that the string represents. To do that, you have to eval it. Because you've got nothing but displays full of literals, you can use the safe ast.literal_eval function to do that. So:

>>> import ast
>>> d = ast.literal_eval(sd)
>>> sd
"{'4': {1, 2}, '2': {1, 2}, '0': {1, 2}}"
>>> d
{'2': {1, 2}, '4': {1, 2}, '0': {1, 2}}

However, you still can't JSON-ify that, because {1, 2} is a set, and JSON doesn't do sets. You have to decide what you want to convert that into. An array? A dict with None values? Something else?

To turn all of the sets into lists (which can be rendered as JSON arrays), you have two choices.

The first is to subclass the JSONEncoder. There's a perfect example right near the top of the docs that does the same thing for encoding complex values as 2-element lists, which you should be able to adapt to your purposes easily: just change the complex to set, and the [o.real, o.imag] to list(o).

The second is to preprocess things. As with the initial parsing, how easy this is depends on how rigid your format is. If all of the top-level values of the dict are sets, and nothing else is a set, it's just {k: list(v) for k, v in sd.items()}. If, on the other hand, you have an arbitrary dict that recursively contains sets along with strings, numbers, dicts, and lists, then you'll probably want to write a recursive function to transform it.

Meanwhile… where did you get this data from? My guess is that you're got some other part of your code that's just printing out a dict (or f.write-ing a str() of a dict…) followed by a list. If so, instead of trying to recover that data later, you should change your code to write JSON (or something else parseable) in the first place.

If your format were a little bit less friendly—if the dict could have lists inside it—you'd need to do something fancier. For example, you could count up open braces minus close braces and keep going until you get back to 0, and that's the dict.