Accepting Arrays in the Query String with Flask

I’ve written an API with Flask that takes some input parameters, does some calculations and returns JSON. Pretty standard. Today I wanted to change it so that some of the parameters could be provided as lists and the API would return results for all combinations. So the original query string would look something like this:

?a=10&b=20&c=hello

which would return:

{
    "a": 10,
    "b": 20,
    "c": "hello",
    "result": 30
}

And I wanted to be able to do this:

?a=10,20&b=20,30&c=hello

which should return:

{
  "data": [
    {
      "a": 10,
      "b": 20,
      "c": "hello",
      "result": 30
    },
    {
      "a": 10,
      "b": 30,
      "c": "hello",
      "result": 40,
    },
    {
      "a": 20,
      "b": 20,
      "c": "hello",
      "result": 40,
    },
    {
      "a": 20,
      "b": 30,
      "c": "hello",
      "result": 50,
    }
  ]
}

• step1: arrays
• step2: ast.literal_eval - feels pretty hacky
• step3: notice what the requests module does
• step4: facilitate that
• result: clearer but more verbose