how to select data from a JSON file in python?

Question

I have a JSON file like that:

[
{
"course": "CMPT 102 D1", 
"instructor": "hamarneh", 
"students": [
  "axc5", 
  "csf10", 
  "ctu1", 
  "nmw15", 
  "nsm12", 
  "ppy1", 
  "qtg13", 
  "tim1", 
  "tkd10", 
  "vhm8", 
  "vsv1", 
  "wps1", 
  "xup12", 
  "yqt6"
], 
"title": "Scientific Cmpt.Prgm"
}]

and here is my code in python:

import json
json_data=open('jsonfile')
data=json.load(json_data)
print(data['students'])

but it shows an error:

   print(data['students'])
   TypeError: list indices must be integers, not str

please help!

And another question: Assume that the JSON file contains many courses with the structure like above. How can I do something like:

Select students, count(course) as course_number from tblstudent
group by students

Print 'data' and see how it looks. I bet it's a list of dicts, not one dict. — sashkello
– sashkello, Commented Oct 3, 2013 at 7:15

Martijn Pieters · Accepted Answer · 2013-10-03 07:23:55Z

5

Your JSON contains a list, with one dictionary in it; there are two square brackets, [ and ], around the dictionary.

Select the first element:

print(data[0]['students'])

Quick demo:

>>> print(data)
[{'instructor': 'hamarneh', 'course': 'CMPT 102 D1', 'title': 'Scientific Cmpt.Prgm', 'students': ['axc5', 'csf10', 'ctu1', 'nmw15', 'nsm12', 'ppy1', 'qtg13', 'tim1', 'tkd10', 'vhm8', 'vsv1', 'wps1', 'xup12', 'yqt6']}]
>>> print(data[0]['students'])
['axc5', 'csf10', 'ctu1', 'nmw15', 'nsm12', 'ppy1', 'qtg13', 'tim1', 'tkd10', 'vhm8', 'vsv1', 'wps1', 'xup12', 'yqt6']

Note that you could have spotted this yourself with a quick print of just data.

If this was a list of multiple courses and you need to count per-student, set up a dictionary keyed on students, containing integers. Using collections.defaultdict() makes that a little easier:

from collections import defaultdict

courses_per_student = defaultdict(int)

for course in data:
    for student in course['students']:
        courses_per_student[student] += 1

edited Oct 3, 2013 at 7:23

answered Oct 3, 2013 at 7:15

Martijn Pieters

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1 Comment

Tung Pham Over a year ago

oh. Thank you. I am very new to JSON. How about if I want to count the number courses each student take as the sql query above?

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