{   "items": [
     "number": {
       "value": 23
       "label": test
    }
]
}

#!/usr/bin/python

import json

myjson = {'items':[]}
d = {}
d['value'] = 23
d['label'] = "test"
myjson.get('items').append(d)
output = json.dumps(myjson)
print output

{
"items": [{
  "value": 23,
  "label": "test"}
]}

{ "items":
    [
       {
       "number":
           {
           "value": 23,
           "label": "test"
           }
       }
    ]
}

jdict = json.loads(yourjson)
 jdict['items'] => [{"number":{...}}]
 jdict['items'][0] => {"number":{...}}
 jdict['items'][0]['number']['value'] => 23

myjson.get('items').append({'number': d})

import json

myjson = {'msg':[]}
d = {}
d['phrase'] = "event1"
d['start'] = "11.22.2018"
d['end'] = "11.28.2018"
myjson.get('msg').append({'phrase': d})
output = json.dumps(myjson)
print(output)

{
  "msg": [
    {
      "phrase": {
        "phrase": "event1",
        "start": "11.22.2018",
        "end": "11.28.2018"
      }
    }
  ]
}

{
  "msg": [
    {
      "phrase": "event1"{
        [
          {
            "start": "11.22.2018",
            "end": "11.28.2018"
          }
          {
            "start": "11.22.2018",
            "end": "11.28.2018"
          }
        ]
      }
    }
  ]
}