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Python JSON dump function

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Python JSON dump function converts the objects into appropriate JSON objects. It is used to write Python serialized objects as JSON formatted data into a file.

json.dump(object, skipkeys=False, ensure_ascii=True, indent=None, allow_nan=True, number_mode = None, datetime_mode = None, separators=None)
  • obj is nothing but a Python serializable object which you want to convert into a JSON format.
  • A fp is a file pointer used to write JSON-formatted data into a file? Python json module always produces string objects, not bytes objects, therefore, fp.write() must support string input.
  • If skipkeys is true (default: False), then dict keys that are not of a basic type, (str, int, float, bool, None) will be skipped instead of raising a TypeError. For example, if one of your dictionary keys is a custom Python object, that key will be omitted while converting the dictionary into JSON.
  • If ensure_ascii is true (the default), the output is guaranteed to have all incoming non-ASCII characters escaped. If ensure_ascii is false, these characters will be output as-is.
  • allow_nan is True by default so their JavaScript equivalents (NaN, Infinity, -Infinity) will be used. If False it will be a ValueError to serialize out-of-range float values (nan, inf, -inf).
  • An indent the argument is used to pretty-print JSON to make it more readable. The default is (', ', ': ') . To get the most compact JSON representation, you should use (',', ':')  to eliminate whitespace.
  • If sort_keys is true (default: False), then the output of dictionaries will be sorted by key

Python JSON dump function example

A simple example code converted the python dictionary to json file format using the JSON package.

import json

dict_pets = {
"Dog": {
"Species": "cocker spaniel",
"country": "United Kingdom"
"Cat": {
"Species": "British Shorthair",
"country": "United Kingdom"
"Hamster": {
"Species": "golden hamster ",
"country": "Turkey"

pets_data = open("pet_data.json", "w")
json.dump(dict_pets, pets_data)


Python JSON dump function example

The json.dump()  is used for following operations

  • Encode Python serialized objects as JSON formatted data.
  • Encode and write Python objects into a JSON file
  • PrettyPrinted JSON data
  • Skip nonbasic types while JSON encoding
  • Perform compact encoding to save file space
  • Handle non-ASCII data while encoding JSON

Mapping between JSON and Python entities while Encoding

list, tuplearray
int, float, int & float-derived Enumsnumber

Do comment if you have any doubts or suggestions on this Python JSON topic.

Note: IDE: PyCharm 2021.3.3 (Community Edition)

Windows 10

Python 3.10.1

All Python Examples are in Python 3, so Maybe its different from python 2 or upgraded versions.

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