Safe composition in python

Question

def json_response(response):
    assert response.code == 200, 'bad http response'
    return json.loads(response.body)

def custom_json_response(response):
    response = json_response(response)
    assert 'answer' in response, 'invalid custom json'
    return response['answer']

The code looks straightforward but I wonder if there any chance to rewrite it to achieve the following:

1. Replace json_response direct call with composition.
2. Code should not become a message from Sirius: everybody should still be able to understand it just without any efforts.
3. It should be robust (composition type safety) yet easy extensible.

Any ideas?

Answer 1

I would not rely on assert. If Python is started with the -O option, then assertions will be stripped out and not evaluated. Better to raise an Exception here.

Answer 2

I'm not sure I'm directly responding to your points, since I don't think I get what you're aiming for, but:

• asserts shouldn't be used for these types of checks (I personally don't use them at all, but if you are going to use them, they're for checking invariants)

• As for what I think you were going for with your composition point, I would just have your second function take an already json.loadsed object (or the return value of your first function) passed in.