accessing to n elements of json file in python

Question

I have a json file which is sorted ascending. I want to access to n elements of it. for example i want to access the last n=5 elements of it. how can i write it?

here is my jason file:

{  
"exDict":[  
  [  
     "android.widget.TextView void setText(int)\n",
     1
  ],
  [  
     "com.android.internal.telephony.cdma.SmsMessage com.android.internal.telephony.cdma.SmsMessage createFromPdu(byte[])\n",
     1
  ],
  [  
     "android.app.AlertDialog$Builder void init(android.content.Context)\n",
     1
  ],
  [  
     "android.location.LocationManager void removeGpsStatusListener(android.location.GpsStatus$Listener)\n",
     6
  ],
  [  
     "android.provider.Settings$Secure java.lang.String getString(android.content.ContentResolver,java.lang.String)\n",
     8
  ],
  [  
     "android.provider.Settings$System int getInt(android.content.ContentResolver,java.lang.String,int)\n",
     9
  ],
  [  
     "android.provider.Settings$System boolean putString(android.content.ContentResolver,java.lang.String,java.lang.String)\n",
     10
  ],
  [  
     "android.database.sqlite.SQLiteDatabase void execSQL(java.lang.String,java.lang.Object[])\n",
     13
  ]
 ]
}

as @salparadise said, the json isn't valid. You can validate it online using this https://jsonformatter.curiousconcept.com/ — Mohamed Ali JAMAOUI, Jul 29 '17 at 06:47
`json.load` just creates a Python structure from the file, usually some mix of dictionary and lists. The standard way to get the last 5 elements of list is `alist[-5:]`. — hpaulj, Jul 29 '17 at 06:57

Mohamed Ali JAMAOUI · Answer 1 · 2017-07-29T08:22:42.393

2

Your data within the dictionary is a list of lists. So, you can simply use list slicing to access the data. Here is a tutorial about slicing

Concretely, for your specific case, you need to load the json file into a dictionary as follows:

import json

with open("/tmp/test.json", "r") as f:
        data = json.load(f)

Then would to get the last n elements, you would do this:

data["exDict"][-5:]

in general to slice n elements where the starting index is start_index, you would do this:

data["exDict"][start_index:n+1]

See this SO (stackoverflow) discussion for a detailed explanation of slicing in python:

Explain slice notation

How to access the first element of each list

Here's a working example, element[0] holds the values of the first element in a list:

import json

with open("/tmp/test.json", "r") as f:
        data = json.load(f)

mylist = data["exDict"][-5:]

# to access the first line element of each list: 
for index, element in enumerate(mylist):
        print element[0]

edited Jul 29 '17 at 08:22

answered Jul 29 '17 at 07:05

Mohamed Ali JAMAOUI

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what is the start index in my sample? – Mas HJ Jul 29 '17 at 07:20
@MasHJ if you want to access any n elements.. you need to specify where to start retreiving these n elements. For you specific case, if you want to slice the first 6 elements you start from 0 – Mohamed Ali JAMAOUI Jul 29 '17 at 07:23
thanks. how can i acces to first element of each line? for example: [ "android.database.sqlite.SQLiteDatabase void execSQL(java.lang.String,java.lang.Object[])\n", 13 ] i want to read just android.database.sqlite.SQLiteDatabase void execSQL(java.lang.String,java.lang.Object[]) – Mas HJ Jul 29 '17 at 08:03
for that line, you do `line[0]` – Mohamed Ali JAMAOUI Jul 29 '17 at 08:05
@MasHJ, if the answer is sufficient for you, you can accept it. – Mohamed Ali JAMAOUI Jul 29 '17 at 08:06

accessing to n elements of json file in python

1 Answers1

How to access the first element of each list