Convert python dictionaries with dates into JSON format

Posted on 21-Dec-2018

Python dictionaries are similar to json format, but they are not JSON. To convert dictionaries to json you'll need to import json module in python.

Consider the following dictionary

# this example is taken from AWS S3 with boto3 library
my_dictionary = {
    'Contents': [
        {
            'Key': 'filename-1.pdf',
            'LastModified': datetime.datetime(2018, 12, 19, 15, 32, 54, tzinfo=tzutc()),
            'Size': 1545033
        },
        {
            'Key': 'filename-2.pdf',
            'LastModified': datetime.datetime(2018, 12, 19, 15, 32, 54, tzinfo=tzutc()),
            'Size': 4222827
        },
        {
            'Key': 'filename-3.pdf',
            'LastModified': datetime.datetime(2018, 12, 19, 15, 32, 54, tzinfo=tzutc()),
            'Size': 640925
        },
        {
            'Key': 'filename-4.pdf',
            'LastModified': datetime.datetime(2018, 12, 19, 15, 32, 54, tzinfo=tzutc()),
            'Size': 1617724
        },
    ]
}

To convert any dictionary to json, first you need to import json module:

import json

Convert simple dictionary into JSON format

Then use json.dumps method:

Note that the following example will output an error if the my_dictionary is provided

import json

simple_dictionary = {
    'Key': 'filename.pdf',
    'Size': 123123
}

data_as_json = json.dumps(simple_dictionary)

print(data_as_json)

The result will be:

{"Key": "filename.pdf", "Size": 123123}

Convert dictionary with datetime in json format

In the above example, if you try to convert the first dictionary that contains datetime object it will output the following error:

TypeError: Object of type datetime is not JSON serializable

To fix this problem we can use a helper function to convert the datetime object into seconds as follows:

import datetime
from dateutil.tz import tzutc
import json

my_dictionary = {
    'Contents': [
        {
            'Key': 'filename-1.pdf',
            'LastModified': datetime.datetime(2018, 12, 19, 15, 32, 54, tzinfo=tzutc()),
            'Size': 1545033
        },
        {
            'Key': 'filename-2.pdf',
            'LastModified': datetime.datetime(2018, 12, 19, 15, 32, 54, tzinfo=tzutc()),
            'Size': 4222827
        },
        {
            'Key': 'filename-3.pdf',
            'LastModified': datetime.datetime(2018, 12, 19, 15, 32, 54, tzinfo=tzutc()),
            'Size': 640925
        },
        {
            'Key': 'filename-4.pdf',
            'LastModified': datetime.datetime(2018, 12, 19, 15, 32, 54, tzinfo=tzutc()),
            'Size': 1617724
        },
    ]
}


def convert_timestamp(item_date_object):
    if isinstance(item_date_object, (datetime.date, datetime.datetime)):
        return item_date_object.timestamp()


my_json_data = json.dumps(my_dictionary, default=convert_timestamp)

print(my_json_data)