a.py

d = {
  "success": True,
  "calendars": [
    {
      "id": 123,
      "year": 2014,
      "months": [
        {
          "id": 50,
          "monthnumber": 1,
          "monthname": "Yanuary 2014",
          "month_days": [
            {
              "id"      : 20,
              "daynumber"   : 1,
              "dayname": "Monday",
              "day_events" : [{
                "id": 1000,
                "name": "MacBook Pro",
                "group": [
                  {
                    "name": "R",
                    "members": [
                      {
                        "name": "foo",
                        "age": 20,
                        "skils": []
                      },
                      {
                        "name": "bar",
                        "age": 22,
                        "skils": [{
                          "name": "art"
                        }]
                      },
                      {
                        "name": "boo",
                        "tel": "12312341212",
                        "age": 20,
                        "skils": []
                      }
                    ]
                  }
                ]
              }]
            },
            {
              "id"      : 21,
              "daynumber"   : 2,
              "dayname": "Thursday",
              "day_events" : [{
                "id": 1001,
                "name": "iPhone"
              }]
            }
          ]
        },{
          "id": 500,
          "monthnumber": 2,
          "monthname": "Febru 2014",
          "month_days": [
            {
              "id"      : 2014,
              "daynumber"   : 1,
              "dayname": "Monday",
              "day_events" : [{
                "id": 100120,
                "name": "MacBook Pro"
              }]
            },
            {
              "id"      : 2231,
              "daynumber"   : 2,
              "dayname": "Thursday",
              "day_events" : [{
                "id": 107701,
                "name": "iPhone"
              }]
            }
          ]
        }
      ]
    },
    {
      "id": 456,
      "year": 2013,
      "months": [
        {
          "id": 50,
          "monthnumber": 1,
          "monthname": "Yanuary 2013",
          "month_days": [
            {
              "id"      : 20,
              "daynumber"   : 10,
              "dayname": "Sunday",
              "day_events" : [{
                "id": 1005,
                "name": "asd 2013"
              }]
            },
            {
              "id"      : 21,
              "daynumber"   : 20,
              "dayname": "Friday",
              "day_events" : [{
                "id": 1008,
                "name": "cvbcv"
              }]
            }
          ]
        }
      ]
    }
  ]
}

def _call(in_dict, out_dict={}):

    for k, v in in_dict.items():

        if isinstance(v, (bool, str, int)):
            out_dict.setdefault(k, True)

        elif isinstance(v, list):
            for i in v:
                out_dict.setdefault(k, {})
                _call(i, out_dict[k])

        elif isinstance(v, dict):
            out_dict[k].setdefault(v, {})
            return _call(v, out_dict[k])

        else:
            print('nothing')

    return out_dict


def _format(d, prefix=''):

    for k, v in d.items():

        if isinstance(v, (bool, str, int)):
            print('{}{}'.format(prefix, k))

        elif isinstance(v, dict):
            prev_prefix = prefix
            prefix += '{}[]__'.format(k)
            _format(v, prefix)
            prefix = prev_prefix

# success
# calendars[]__id
# calendars[]__year
# calendars[]__months[]__id
# calendars[]__months[]__monthnumber
# calendars[]__months[]__monthname
# calendars[]__months[]__month_days[]__id
# calendars[]__months[]__month_days[]__daynumber
# calendars[]__months[]__month_days[]__dayname
# calendars[]__months[]__month_days[]__day_events[]__id
# calendars[]__months[]__month_days[]__day_events[]__name
# calendars[]__months[]__month_days[]__day_events[]__group[]__name
# calendars[]__months[]__month_days[]__day_events[]__group[]__members[]__name
# calendars[]__months[]__month_days[]__day_events[]__group[]__members[]__age
# calendars[]__months[]__month_days[]__day_events[]__group[]__members[]__skils[]__name
# calendars[]__months[]__month_days[]__day_events[]__group[]__members[]__tel


# print(_format(_call(d)))
from pprint import pprint
pprint(_call(d))
_format(_call(d))

{'calendars': {'id': True,
               'months': {'id': True,
                          'month_days': {'day_events': {'group': {'members': {'age': True,
                                                                              'name': True,
                                                                              'skils': {'name': True},
                                                                              'tel': True},
                                                                  'name': True},
                                                        'id': True,
                                                        'name': True},
                                         'dayname': True,
                                         'daynumber': True,
                                         'id': True},
                          'monthname': True,
                          'monthnumber': True},
               'year': True},
 'success': True}
calendars[]__months[]__monthnumber
calendars[]__months[]__monthname
calendars[]__months[]__id
calendars[]__months[]__month_days[]__day_events[]__group[]__name
calendars[]__months[]__month_days[]__day_events[]__group[]__members[]__age
calendars[]__months[]__month_days[]__day_events[]__group[]__members[]__tel
calendars[]__months[]__month_days[]__day_events[]__group[]__members[]__name
calendars[]__months[]__month_days[]__day_events[]__group[]__members[]__skils[]__name
calendars[]__months[]__month_days[]__day_events[]__id
calendars[]__months[]__month_days[]__day_events[]__name
calendars[]__months[]__month_days[]__dayname
calendars[]__months[]__month_days[]__daynumber
calendars[]__months[]__month_days[]__id
calendars[]__id
calendars[]__year
success