Re: Web services input validation problem

It's Moodle 2.4.

I've made some progress with the problem - it actually required one more level of arrays, like this:

array(

    'courseid' => 10,
    'grades' => array(
        array(
            array(
                'grade' => 50.0,
                'userid' => 20
            ),
        ),
         array(
            array(
                'grade' => 50.0,
                'userid' => 19
            ),
        ),
    )
)

Don't ask my why, because I don't know - it's just a random thing I tried out of desperation and it got me  a bit further.

Now I'm stuck with:

grades => Invalid parameter value detected: Only arrays accepted. The bad value is: '{'grade': 50, 'userid': 20}'.
I know it looks like json, but I'm not POSTin json, but a Python dictionary (rough equivalent of PHP associative array). 
Is there a way I could json_decode before validation? I could just send json and skip the whole format issue..