Just use normal dictionaries in python when constructing the JSON then use the JSON package to export to JSON files.

You can construct them like this (long way):

a_dict = {}
a_dict['id'] = {}
a_dict['id']['a'] = {'properties' : {}}
a_dict['id']['a']['properties']['x'] = '9'
a_dict['id']['a']['properties']['y'] = '3'
a_dict['id']['a']['properties']['z'] = '17'
a_dict['id']['b'] = {'properties' : {}}
a_dict['id']['b']['properties']['x'] = '3'
a_dict['id']['b']['properties']['y'] = '2'
a_dict['id']['b']['properties']['z'] = '1'

or you can use a function:

def dict_construct(id, x, y, z):
 new_dic = {id : {'properties': {} } }
 values = [{'x': x}, {'y': y}, {'z':z}]
 for val in values:
    new_dic[id]['properties'].update(val)
 return new_dic

return_values = [('a', '9', '3', '17'), ('b', '3', '2', '1')]

a_dict = {'id': {} }
for xx in return_values:
    add_dict = dict_construct(*xx)
    a_dict['id'].update(add_dict)

print(a_dict)

both give you as a dictionary:

{'id': {'a': {'properties': {'x': '9', 'y': '3', 'z': '17'}}, 'b': {'properties': {'x': '3', 'y': '2', 'z': '1'}}}}

using json.dump:

with open('data.json', 'w') as outfile:
    json.dump(a_dict, outfile)

you get as a file:

{
  "id": {
    "a": {
      "properties": {
        "x": "9",
        "y": "3",
        "z": "17"
      }
    },
    "b": {
      "properties": {
        "x": "3",
        "y": "2",
        "z": "1"
      }
    }
  }
}

data is a Python dictionary. It needs to be encoded as JSON before writing.

Use this for maximum compatibility (Python 2 and 3):

import json
with open('data.json', 'w') as f:
    json.dump(data, f)

On a modern system (i.e. Python 3 and UTF-8 support), you can write a nicer file using:

import json
with open('data.json', 'w', encoding='utf-8') as f:
    json.dump(data, f, ensure_ascii=False, indent=4)

See json documentation.