从字符串中获取某些信息

Question

I'm new to python as was wondering how I could get the estimatedWait and routeName from this string.

{
  "lastUpdated": "07:52",
  "filterOut": [],
  "arrivals": [
    {
      "routeId": "B16",
      "routeName": "B16",
      "destination": "Kidbrooke",
      "estimatedWait": "due",
      "scheduledTime": "06: 53",
      "isRealTime": true,
      "isCancelled": false
    },
    {
      "routeId":"B13",
      "routeName":"B13",
      "destination":"New Eltham",
      "estimatedWait":"29 min",
      "scheduledTime":"07:38",
      "isRealTime":true,
      "isCancelled":false
    }
  ],
  "serviceDisruptions":{
    "infoMessages":[],
    "importantMessages":[],
    "criticalMessages":[]
  }
}

And then save this to another string which would be displayed on the lxterminal of the raspberry pi 2. I would like only the 'routeName' of B16 to be saved to the string. How do I do that?

Answer 1

You just have to deserialise the object and then use the index to access the data you want.

To find only the B16 entries you can filter the arrivals list.

import json
obj = json.loads(json_string)

# filter only the b16 objects
b16_objs = filter(lambda a: a['routeName'] == 'B16',  obj['arrivals'])

if b16_objs:
    # get the first item
    b16 = b16_objs[0]
    my_estimatedWait = b16['estimatedWait']
    print(my_estimatedWait)

Answer 2

You can use string.find() to get the indices of those value identifiers and extract them.

Example:

def get_vaules(string):
    waitIndice = string.find('"estimatedWait":"')
    routeIndice = string.find('"routeName":"')
    estimatedWait = string[waitIndice:string.find('"', waitIndice)]
    routeName = string[routeIndice:string.find('"', routeIndice)]
    return estimatedWait, routeName

Or you could just deserialize the json object (highly recommended)

import json

def get_values(string):
    jsonData = json.loads(string)
    estimatedWait = jsonData['arrivals'][0]['estimatedWait']
    routeName = jsonData['arrivals'][0]['routeName']
    return estimatedWait, routeName

Parsing values from a JSON file using Python?