How to dump a dict to a JSON file?

Question

I have a dict like this:

sample = {'ObjectInterpolator': 1629,  'PointInterpolator': 1675, 'RectangleInterpolator': 2042}

I can't figure out how to dump the dict to a JSON file as showed below:

{      
    "name": "interpolator",
    "children": [
      {"name": "ObjectInterpolator", "size": 1629},
      {"name": "PointInterpolator", "size": 1675},
      {"name": "RectangleInterpolator", "size": 2042}
     ]
}

Is there a pythonic way to do this?

You may guess that I want to generate a d3 treemap.

is it possible for you to accept one of the answers? – Robson Feb 18 '22 at 12:34 — Robson, Feb 18 '22 at 12:34

moobi · Answer 1 · 2017-05-02T14:45:22.193

635

import json
with open('result.json', 'w') as fp:
    json.dump(sample, fp)

This is an easier way to do it.

In the second line of code the file result.json gets created and opened as the variable fp.

In the third line your dict sample gets written into the result.json!

edited May 02 '17 at 14:45

answered Sep 26 '14 at 10:22

moobi

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@Fermi the result JSON is sorted one.how can I stop this sortin while dumping it into a JSON – Jun 13 '16 at 07:34
1

@Danish Don't know. Unless there is a question already on SO about your problem, you should create a new question describing your issue. (btw, i m simply an editor of those posts) – user Jun 13 '16 at 13:22
I also dont know. Just ask a new question like Fermi proposed. – moobi Jun 13 '16 at 17:18
14

Tip : If you don't want to write to a file, and only see the output, try redirecting it to `stdout: json.dump('SomeText', sys.stdout)` – Arindam Roychowdhury Dec 14 '16 at 08:48
2

@Dan-ish Have you tried json.dump(sample, fp, sort_keys=False ) ? Assuming I understand what you mean. – Chris Larson Dec 26 '16 at 05:18
3

Good thing to remember here is that unless you use an `OrderedDict` (python >2.7) there is no guarantee that keys are ordered in any particular manner – ford prefect Aug 01 '17 at 18:08
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It throws " dumps() takes 1 positional argument but 2 were given" error – Vijay Nirmal Aug 08 '18 at 19:18
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@Vijay, the function is called `dump` (not `dumps`). – moobi Aug 09 '18 at 20:06
What if my values of dictionary is a Set() , – BreakBadSP Mar 26 '19 at 15:54
FileNotFoundError: [Errno 2] No such file or directory – Joe Huang Apr 22 '21 at 20:16
Note that you can pass the 'indent' parameter (usually 2 or 4 is recommended) to `dump()`, so your JSON file is human readable. – Raleigh L. May 25 '22 at 23:55

holys · Answer 2 · 2013-06-12T08:28:15.180

54

Combine the answer of @mgilson and @gnibbler, I found what I need was this:


d = {"name":"interpolator",
     "children":[{'name':key,"size":value} for key,value in sample.items()]}
j = json.dumps(d, indent=4)
f = open('sample.json', 'w')
print >> f, j
f.close()

It this way, I got a pretty-print json file. The tricks print >> f, j is found from here: http://www.anthonydebarros.com/2012/03/11/generate-json-from-sql-using-python/

edited Jun 12 '13 at 08:28

answered Jun 12 '13 at 08:17

holys

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`print(j, file=f)` in Python 3.6 (instead of `print >> f, j`) – mjkrause Dec 29 '17 at 15:06
2

`print(j, file=f)` didn't work for me,I didn't need to do the J part as well. `d = {'a':1, 'b':2} print(d, file=open('sample.json', 'wt'))` worked. – H S Rathore May 23 '20 at 07:08
You can also use `indent` to create formatted dump: `json.dump(content, file, indent=4)` – deshu Feb 10 '22 at 15:37

score 26 · Answer 3 · answered Jun 11 '13 at 12:18

26

d = {"name":"interpolator",
     "children":[{'name':key,"size":value} for key,value in sample.items()]}
json_string = json.dumps(d)

Of course, it's unlikely that the order will be exactly preserved ... But that's just the nature of dictionaries ...

answered Jun 11 '13 at 12:18

mgilson

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json_string = json.dumps(d, , sort_keys=True) if sorted order is desired. – Chris Larson Dec 26 '16 at 05:20

score 18 · Answer 4 · answered Jun 11 '13 at 12:17

This should give you a start

>>> import json
>>> print json.dumps([{'name': k, 'size': v} for k,v in sample.items()], indent=4)
[
    {
        "name": "PointInterpolator",
        "size": 1675
    },
    {
        "name": "ObjectInterpolator",
        "size": 1629
    },
    {
        "name": "RectangleInterpolator",
        "size": 2042
    }
]

score 15 · Answer 5 · answered May 04 '20 at 06:37

15

with pretty-print format:

import json

with open(path_to_file, 'w') as file:
    json_string = json.dumps(sample, default=lambda o: o.__dict__, sort_keys=True, indent=2)
    file.write(json_string)

answered May 04 '20 at 06:37

jmhostalet

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you can supply all those parameters to `dump(sample, file, ...)` too. The extra step of writing to a string is not needed. `dump` internally writes in chunks. This could be more efficient than to compile a (possibly huge) string first. – Adrian W Jul 02 '20 at 10:46

als0052 · Answer 6 · 2021-11-05T11:14:56.443

Also wanted to add this (Python 3.7)

import json

with open("dict_to_json_textfile.txt", 'w') as fout:
    json_dumps_str = json.dumps(a_dictionary, indent=4)
    print(json_dumps_str, file=fout)

Update (11-04-2021): So the reason I added this example is because sometimes you can use the print() function to write to files, and this also shows how to use the indentation (unindented stuff is evil!!). However I have recently started learning about threading and some of my research has shown that the print() statement is not always thread-safe. So if you need threading you might want to be careful with this one.

score 3 · Answer 7 · answered Sep 10 '20 at 15:28

3

If you're using Path:

example_path = Path('/tmp/test.json')
example_dict = {'x': 24, 'y': 25}
json_str = json.dumps(example_dict, indent=4) + '\n'
example_path.write_text(json_str, encoding='utf-8')

answered Sep 10 '20 at 15:28

davidvandebunte

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How to dump a dict to a JSON file?

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